Seed household settings at boot and serve the settings API

On first boot create the single household_settings row with the zone from
MEALQUEST_DEFAULT_TZ and the seed times and days (dinner 17:30, reminder
16:30, rotation check 09:00, plan draft Fri 09:00, suggestions Sun 08:00,
chat autosend Sat 08:00). Boot fails if the row is missing and the zone is
unset; an existing row is never overwritten. Config validates the zone
whenever it is set.

Add household.SettingsService with Get, a validating Update (IANA zone,
zero-padded 24-hour HH:MM, day of week 0-6) that records updated_by, and
in-process Subscribe for the scheduler. Serve it as GET and PATCH
/api/v1/settings/household; invalid input is a 400 in the standard error
body. Migration 0002 adds household_settings.updated_by, and
internal/actor carries the member name in the request context.

Link time/tzdata from internal/household so zones load in the minimal
image, which has no system zone database.

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

internal/config/config_test.go

@@ -55,6 +55,25 @@ func TestLoad(t *testing.T) {
 			name: "all required vars present",
 			env:  valid(),
 		},
+		{
+			name: "default time zone set",
+			env:  with(map[string]string{EnvDefaultTZ: "America/New_York"}),
+		},
+		{
+			name:    "default time zone not an IANA zone",
+			env:     with(map[string]string{EnvDefaultTZ: "Mars/Olympus_Mons"}),
+			badVars: []string{EnvDefaultTZ},
+		},
+		{
+			name:    "default time zone set but empty",
+			env:     with(map[string]string{EnvDefaultTZ: ""}),
+			badVars: []string{EnvDefaultTZ},
+		},
+		{
+			name:    "default time zone Local refused",
+			env:     with(map[string]string{EnvDefaultTZ: "Local"}),
+			badVars: []string{EnvDefaultTZ},
+		},
 		{
 			name:    "one missing",
 			env:     with(nil, EnvHTTPAddr),
@@ -232,6 +251,7 @@ func TestLoadValues(t *testing.T) {
 		EnvDataDir:         dir,
 		EnvShutdownTimeout: "1m30s",
 		EnvSecretKeyFile:   secretPath,
+		EnvDefaultTZ:       "Europe/London",
 	}
 	cfg, err := load(func(k string) (string, bool) { v, ok := env[k]; return v, ok })
 	if err != nil {
@@ -253,6 +273,9 @@ func TestLoadValues(t *testing.T) {
 	if cfg.SecretKey.Reveal() != "s3cret-value" {
 		t.Errorf("SecretKey.Reveal() = %q, want trailing newline trimmed", cfg.SecretKey.Reveal())
 	}
+	if cfg.DefaultTZ != "Europe/London" {
+		t.Errorf("DefaultTZ = %q, want Europe/London", cfg.DefaultTZ)
+	}
 }
 
 func TestSecretRedacted(t *testing.T) {