Implement activity log (task 22)

- activity_log table in _core/schema.ts with household+created_at index;
  migration 0008_activity_log.sql applied
- logActivity() in _core/activity.ts reads current session and inserts a row
- ActivityLogEntry type + renderActivity?(entry): string added to
  EntityTypeRegistration so modules declare human-readable labels without
  any if/else branches in the widget
- core.activity widget replaced with a real async server component that
  queries the last 20 rows and renders via the registry
- logActivity wired into every create/update/delete in calendar, lists,
  and notes server actions; getAuthorizedItem also returns text so
  toggle/delete can include item text in the payload
- pnpm typecheck, lint, build, and all 4 E2E specs pass

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/modules/_core/index.ts

@@ -8,6 +8,8 @@ export type {
   ReminderCapabilities,
   SearchAdapter,
   SearchResult,
+  ActivityLogEntry,
 } from "./module";
 export { registerModule, getRegistry, getEntityType, getWidget, getQuickAdds } from "./registry";
 export type { QuickAddItem, SerializedQuickAddItem } from "./registry";
+export { logActivity } from "./activity";