AppForge: migrate off Supabase to external Postgres + Better Auth + local storage

- New Express + TypeScript backend (server/) with pg, Better Auth, local file storage
- De-Supabased Postgres schema (server/db) and TS reimplementations of DB functions
- Frontend data layer rewired to REST (rest-client + backend-client compat shim)
- Removed all Supabase references (code, config, deps, docs)
- New brand assets: gradient favicon/app icons + dark/white wordmark logos

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/src/lib/roles.ts

@@ -0,0 +1,29 @@
+import { one } from '../db.js';
+
+export type AppRole = 'admin' | 'moderator' | 'user';
+
+/** Reimplements public.has_role(uuid, app_role). */
+export async function hasRole(userId: string, role: AppRole): Promise<boolean> {
+  const row = await one<{ exists: boolean }>(
+    `SELECT EXISTS (SELECT 1 FROM public.user_roles WHERE user_id = $1 AND role = $2) AS exists`,
+    [userId, role]
+  );
+  return !!row?.exists;
+}
+
+/** Reimplements public.get_user_role(uuid). Returns null if none. */
+export async function getUserRole(userId: string): Promise<AppRole | null> {
+  const row = await one<{ role: AppRole }>(
+    `SELECT role FROM public.user_roles WHERE user_id = $1 LIMIT 1`,
+    [userId]
+  );
+  return row?.role ?? null;
+}
+
+/** Reimplements public.no_admin_exists(). */
+export async function noAdminExists(): Promise<boolean> {
+  const row = await one<{ exists: boolean }>(
+    `SELECT NOT EXISTS (SELECT 1 FROM public.user_roles WHERE role = 'admin') AS exists`
+  );
+  return !!row?.exists;
+}