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>

public/favicon-maskable.svg

@@ -0,0 +1,13 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" width="512" height="512" role="img" aria-label="AppForge">
+  <defs>
+    <linearGradient id="afgm" x1="0" y1="0" x2="1" y2="1">
+      <stop offset="0" stop-color="#8B5CF6"/>
+      <stop offset="0.55" stop-color="#6366F1"/>
+      <stop offset="1" stop-color="#0EA5E9"/>
+    </linearGradient>
+  </defs>
+  <!-- full-bleed background for Android maskable safe zone -->
+  <rect x="0" y="0" width="512" height="512" fill="url(#afgm)"/>
+  <path d="M300 136 L182 316 H256 L242 392 L334 248 H272 Z"
+        fill="#ffffff" stroke="#ffffff" stroke-width="5" stroke-linejoin="round"/>
+</svg>