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/actor/actor_test.go

@@ -0,0 +1,16 @@
+package actor
+
+import (
+	"context"
+	"testing"
+)
+
+func TestFrom(t *testing.T) {
+	t.Parallel()
+	if got := From(context.Background()); got != "" {
+		t.Errorf("From(empty context) = %q, want empty", got)
+	}
+	if got := From(With(context.Background(), "sam")); got != "sam" {
+		t.Errorf("From(With(sam)) = %q, want sam", got)
+	}
+}