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/robots.txt

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+User-agent: Googlebot
+Allow: /
+
+User-agent: Bingbot
+Allow: /
+
+User-agent: Twitterbot
+Allow: /
+
+User-agent: facebookexternalhit
+Allow: /
+
+User-agent: *
+Allow: /