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>

drizzle/0008_activity_log.sql

@@ -0,0 +1,16 @@
+CREATE TABLE "activity_log" (
+	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+	"household_id" uuid NOT NULL,
+	"entity_type" text NOT NULL,
+	"entity_id" uuid NOT NULL,
+	"actor_id" uuid NOT NULL,
+	"action" text NOT NULL,
+	"payload" jsonb,
+	"created_at" timestamp with time zone DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+ALTER TABLE "activity_log" ADD CONSTRAINT "activity_log_household_id_households_id_fk" FOREIGN KEY ("household_id") REFERENCES "public"."households"("id") ON DELETE cascade ON UPDATE no action;
+--> statement-breakpoint
+ALTER TABLE "activity_log" ADD CONSTRAINT "activity_log_actor_id_users_id_fk" FOREIGN KEY ("actor_id") REFERENCES "public"."users"("id") ON DELETE cascade ON UPDATE no action;
+--> statement-breakpoint
+CREATE INDEX "activity_log_household_created_idx" ON "activity_log" USING btree ("household_id","created_at");