refactor: remove dead code identified by knip

Delete unused Fab component (superseded by QuickAddFab), unused server
actions and queries (listDashboards, reorderDashboards, deleteCareLog,
canAccessContainer, getOverduePlants, getCareDueSoon, addItemToDefaultList,
reorderItems, getOrCreateDefaultList), unused helpers (getCurrentUser,
BrandWordmark, TopbarSpacer, DEV_LOGIN_COOKIE, no-arg ensureDefault*
wrappers, addListItem re-export), and drop export keyword from five
internal-only functions.

Verified with typecheck, eslint, and production build after each removal.

src/modules/calendar/server/defaults.ts

@@ -1,6 +1,6 @@
 import { and, eq } from "drizzle-orm";
 import { db } from "@/lib/db";
-import { householdMembers, households, users } from "@/modules/_core/schema";
+import { householdMembers } from "@/modules/_core/schema";
 import { calendars } from "../schema";
 
 const HOME_COLOR = "#2563eb";
@@ -17,22 +17,6 @@ export async function ensureDefaultCalendarsForMembership({
   await ensurePersonalCalendar({ householdId, userId });
 }
 
-export async function ensureDefaultCalendars() {
-  const householdRows = await db.select().from(households);
-  for (const household of householdRows) {
-    await ensureHomeCalendar(household.id);
-  }
-
-  const memberships = await db
-    .select({ householdId: householdMembers.householdId, userId: users.id })
-    .from(householdMembers)
-    .innerJoin(users, eq(householdMembers.userId, users.id));
-
-  for (const membership of memberships) {
-    await ensurePersonalCalendar(membership);
-  }
-}
-
 async function ensureHomeCalendar(householdId: string) {
   const [existing] = await db
     .select({ id: calendars.id })