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/db/models.go

@@ -85,6 +85,7 @@ type HouseholdSetting struct {
 	UpdatesSeenAt         sql.NullString
 	CreatedAt             string
 	UpdatedAt             string
+	UpdatedBy             sql.NullString
 }
 
 type IntegrationsGoogle struct {