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Delete unused Fab component (superseded by QuickAddFab), unused server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/app/d/actions.ts

@@ -19,22 +19,6 @@ export type DashboardMeta = {
   position: number;
 };
 
-export async function listDashboards(): Promise<DashboardMeta[]> {
-  const { user } = await getCurrentSession();
-  const rows = await db
-    .select({
-      id: dashboards.id,
-      name: dashboards.name,
-      slug: dashboards.slug,
-      isDefault: dashboards.isDefault,
-      position: dashboards.position,
-    })
-    .from(dashboards)
-    .where(eq(dashboards.userId, user.id))
-    .orderBy(asc(dashboards.position), asc(dashboards.createdAt));
-  return rows;
-}
-
 export async function getDefaultDashboardSlug(): Promise<string> {
   const { user } = await getCurrentSession();
   const rows = await db
@@ -160,19 +144,6 @@ export async function setDefaultDashboard(id: string): Promise<void> {
   revalidatePath("/");
 }
 
-export async function reorderDashboards(orderedIds: string[]): Promise<void> {
-  const { user } = await getCurrentSession();
-  await Promise.all(
-    orderedIds.map((id, i) =>
-      db
-        .update(dashboards)
-        .set({ position: i })
-        .where(and(eq(dashboards.id, id), eq(dashboards.userId, user.id))),
-    ),
-  );
-  revalidatePath("/");
-}
-
 export async function saveDashboardLayout(id: string, layout: DashboardLayout): Promise<void> {
   const { user } = await getCurrentSession();
   // Validate each widget's config against its registered schema