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/household/zone.go

@@ -0,0 +1,28 @@
+package household
+
+import (
+	"errors"
+	"fmt"
+	"time"
+
+	// Embeds the IANA zone database in the binary, so zones load the same
+	// way in a minimal image with no /usr/share/zoneinfo.
+	_ "time/tzdata"
+)
+
+// LoadZone loads the IANA zone name, such as "America/New_York". The empty
+// name and "Local", which time.LoadLocation maps to UTC and the process zone,
+// are refused: the household zone is never implied.
+func LoadZone(name string) (*time.Location, error) {
+	if name == "" {
+		return nil, errors.New("time zone is empty (want an IANA zone such as America/New_York)")
+	}
+	if name == "Local" {
+		return nil, errors.New(`time zone "Local" is not an IANA zone (want e.g. America/New_York)`)
+	}
+	loc, err := time.LoadLocation(name)
+	if err != nil {
+		return nil, fmt.Errorf("unknown time zone %q (want an IANA zone such as America/New_York)", name)
+	}
+	return loc, nil
+}