Seed household settings at boot and serve the settings API

Port of Feature 04 task 3 (7629cab) onto Feature 04 + Feature 03.

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). An existing row is never overwritten.

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. Link time/tzdata
from internal/household so zones load in the minimal image.

Review fixes:
- F1: the settings routes are mounted on the protected /api/v1 subrouter,
  so they need a session (RequireSession) and, for PATCH, the CSRF token.
  updated_by is the session actor's subject from auth.ActorFrom; the
  duplicate internal/actor package is dropped, and Update refuses an empty
  member instead of storing NULL. A test drives PATCH through the
  production router with a real SessionManager session.
- F2: config no longer validates MEALQUEST_DEFAULT_TZ. Seeding requires a
  valid zone only when it creates the row (ErrNoDefaultZone,
  ErrInvalidDefaultZone, both naming the variable at boot), so a reboot
  over existing settings ignores a missing or invalid default.

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

internal/server/csrf_test.go

@@ -34,9 +34,10 @@ func TestCSRFThroughRouter(t *testing.T) {
 		{"PATCH without header", http.MethodPatch, "/api/v1/settings/household", nil, http.StatusForbidden, csrfJSON},
 		{"DELETE with wrong header", http.MethodDelete, "/api/v1/me", []string{"wrong-token"}, http.StatusForbidden, csrfJSON},
 		// The right token passes the check and reaches the router, which has
-		// no POST /api/v1/me.
+		// no POST /api/v1/me, and the settings handler, which refuses the
+		// empty body.
 		{"POST with right header", http.MethodPost, "/api/v1/me", []string{testSession.CSRFToken}, http.StatusMethodNotAllowed, methodNotAllowedJSON},
-		{"PATCH with right header", http.MethodPatch, "/api/v1/settings/household", []string{testSession.CSRFToken}, http.StatusNotFound, notFoundJSON},
+		{"PATCH with right header", http.MethodPatch, "/api/v1/settings/household", []string{testSession.CSRFToken}, http.StatusBadRequest, `{"error":{"code":"invalid_request","message":"request body must be a JSON object","retryable":false}}`},
 		{"GET without header", http.MethodGet, "/api/v1/me", nil, http.StatusOK, ""},
 		// Only GET is exempt; HEAD and OPTIONS need the header too.
 		{"HEAD without header", http.MethodHead, "/api/v1/me", nil, http.StatusForbidden, csrfJSON},