Add real backend: JWT auth, SQLite user storage, server-side file uploads

[Copilot]

Login was entirely frontend-simulated with no persistence. This adds a Node.js/Express backend with real auth, a SQLite database, and authenticated file uploads.

Backend (server/)

• server/index.js — Express API with:
  • POST /api/auth/register / POST /api/auth/login — bcrypt-hashed passwords, JWT (7-day) response
  • GET /api/auth/me — token validation for session restore
  • POST /api/upload — multer-based image/audio upload (20 MB limit, mime-type validated), stored under server/uploads/, recorded in DB
  • SQLite schema (users, uploads) auto-created via better-sqlite3
  • Rate limiting on all routes via express-rate-limit (20 req/15 min auth, 10 req/min upload)
  • Production guard: throws at startup if JWT_SECRET env var is unset when NODE_ENV=production

Frontend

• Login.js — Login/Register tabs; calls real API via axios; stores JWT in localStorage; surfaces server error messages
• App.js — Restores session on mount via GET /api/auth/me; clears JWT on logout; removed Google-login stub
• AdminPanel.js — POSTs files to /api/upload with ******; shows local blob preview immediately while upload completes async

Config

• Root package.json: "proxy": "http://localhost:5000", npm run dev via concurrently, npm run server
• .gitignore: excludes server/uploads/ and server/blebetalo.db

npm run dev   # Express on :5000 + React on :3000

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