Add Google Chat webhook sender and settings API (Feature 19)

internal/chat keeps the incoming webhook in chat_settings, sealed with
secretbox, and is the notify sender of the chat channel.

- PUT /api/v1/settings/chat-webhook {url, space_label} accepts only
  https://chat.googleapis.com/v1/spaces/{space}/messages?key=…&token=…;
  GET answers the space label, a masked URL tail and the last test outcome.
- POST /api/v1/settings/chat-webhook/test posts "MealQuest · test message",
  answers Google Chat's HTTP status and records last_test_at/status.
- Notifications post {text}, plus cardsV2 with an "Open" button under
  MEALQUEST_PUBLIC_URL for plan_ready and list_ready, threaded by
  threadKey=mealquest-week-YYYY-Www with
  REPLY_MESSAGE_FALLBACK_TO_NEW_THREAD. 429 and 5xx are retried; any other
  non-2xx fails the row at once through the new notify.ErrUndeliverable.
- One place builds every event's title, body and Chat text.

The webhook URL never appears in a response, log line or error; tests
against an httptest Chat endpoint scan both.

Maestro task 919e9422-3a41-4f1f-8967-77da17f5f9f3.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/server/server_test.go

@@ -54,7 +54,7 @@ func newTestRouterWith(t *testing.T, version string, settings *household.Setting
 		"index.html":             {Data: []byte(fixtureIndex)},
 		"assets/index-AbC123.js": {Data: []byte(fixtureAsset)},
 	}
-	r, err := NewRouter(logger, version, nil, stubAuth{}, stubSessions{}, settings, newTestSearch(t), newTestAI(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), runner, newTestPhotos(t), assets)
+	r, err := NewRouter(logger, version, nil, stubAuth{}, stubSessions{}, settings, newTestSearch(t), newTestAI(t), newTestChat(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), runner, newTestPhotos(t), assets)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -287,7 +287,7 @@ func TestNewRouterRequiresAISettings(t *testing.T) {
 	t.Parallel()
 
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), nil, newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
+	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), nil, newTestChat(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
 		t.Fatal("NewRouter accepted a nil AI settings service")
 	}
 }
@@ -296,7 +296,7 @@ func TestNewRouterRequiresSearchSettings(t *testing.T) {
 	t.Parallel()
 
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), nil, newTestAI(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
+	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), nil, newTestAI(t), newTestChat(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
 		t.Fatal("NewRouter accepted a nil recipe search settings service")
 	}
 }
@@ -305,7 +305,7 @@ func TestNewRouterRequiresPhotoFiles(t *testing.T) {
 	t.Parallel()
 
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), nil, fstest.MapFS{"index.html": {}}); err == nil {
+	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestChat(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), nil, fstest.MapFS{"index.html": {}}); err == nil {
 		t.Fatal("NewRouter accepted nil photo files")
 	}
 }
@@ -314,7 +314,7 @@ func TestNewRouterRequiresSettings(t *testing.T) {
 	t.Parallel()
 
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, nil, newTestSearch(t), newTestAI(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
+	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, nil, newTestSearch(t), newTestAI(t), newTestChat(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
 		t.Fatal("NewRouter accepted a nil settings service")
 	}
 }
@@ -323,7 +323,7 @@ func TestNewRouterRequiresDinners(t *testing.T) {
 	t.Parallel()
 
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), nil, newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
+	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestChat(t), nil, newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
 		t.Fatal("NewRouter accepted a nil dinners service")
 	}
 }
@@ -332,7 +332,7 @@ func TestNewRouterRequiresSuggestions(t *testing.T) {
 	t.Parallel()
 
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestDinners(t), nil, newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
+	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestChat(t), newTestDinners(t), nil, newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
 		t.Fatal("NewRouter accepted a nil suggestions service")
 	}
 }
@@ -341,7 +341,7 @@ func TestNewRouterRequiresPlan(t *testing.T) {
 	t.Parallel()
 
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestDinners(t), newTestSuggest(t), nil, newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
+	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestChat(t), newTestDinners(t), newTestSuggest(t), nil, newTestShopping(t), newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
 		t.Fatal("NewRouter accepted a nil plan service")
 	}
 }
@@ -350,7 +350,7 @@ func TestNewRouterRequiresShopping(t *testing.T) {
 	t.Parallel()
 
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), nil, newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
+	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestChat(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), nil, newTestGoogle(t), newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
 		t.Fatal("NewRouter accepted a nil shopping service")
 	}
 }
@@ -359,7 +359,7 @@ func TestNewRouterRequiresGoogle(t *testing.T) {
 	t.Parallel()
 
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), nil, newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
+	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestChat(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), nil, newTestPush(t), newTestRunner(t), newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
 		t.Fatal("NewRouter accepted a nil Google Calendar service")
 	}
 }
@@ -368,7 +368,7 @@ func TestNewRouterRequiresJobRunner(t *testing.T) {
 	t.Parallel()
 
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
-	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), nil, newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
+	if _, err := NewRouter(logger, "dev", nil, stubAuth{}, stubSessions{}, newTestSettings(t), newTestSearch(t), newTestAI(t), newTestChat(t), newTestDinners(t), newTestSuggest(t), newTestPlan(t), newTestShopping(t), newTestGoogle(t), newTestPush(t), nil, newTestPhotos(t), fstest.MapFS{"index.html": {}}); err == nil {
 		t.Fatal("NewRouter accepted a nil job runner")
 	}
 }