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>

README.md

@@ -44,6 +44,7 @@ export MEALQUEST_OIDC_ALLOWED_GROUPS=mealquest-admin
 # X-Forwarded-For/-Proto headers are honoured (production: Traefik). Unset
 # trusts no peer, which is right for local development.
 # export MEALQUEST_TRUSTED_PROXY=10.60.1.33
+export MEALQUEST_DEFAULT_TZ=America/New_York
 make dev
 ```
 
@@ -51,11 +52,16 @@ make dev
 (which proxies `/api`, `/auth` and `/media` to `:8080`). Open
 http://localhost:5173. Configuration is environment-only and fails fast:
 every variable above is required except the commented-out session
-lifetimes (when set they must be positive, with MAX at least IDLE) and
-trusted proxy list (every entry must be an IP or CIDR), and
+lifetimes (when set they must be positive, with MAX at least IDLE),
+trusted proxy list (every entry must be an IP or CIDR) and
+`MEALQUEST_DEFAULT_TZ`, and
 secrets are read only from files named by `*_FILE` variables. `MEALQUEST_PUBLIC_URL`, `MEALQUEST_OIDC_ISSUER` and the
 endpoints the issuer advertises must be `https://`; plain `http://` is
 accepted only for `localhost`, `127.0.0.1` and `[::1]`.
+`MEALQUEST_DEFAULT_TZ` is the IANA zone the household settings are created
+with on first boot: until those settings exist, boot fails unless it is a
+valid IANA zone. Later boots ignore it, set or not (change the zone in
+household settings instead).
 
 ## Common commands