feat: web admin panel + better-sqlite3 migration + Docker fixes
- Added Express.js admin panel on port 3001 (ADMIN_PORT env)
- Dashboard: stats (users, products, purchases, revenue)
- Users: list, details, ban/unban toggle
- Products: CRUD by category
- Wallets: list with balances
- Purchases: history with filters
- Audit log: view audit trail
- Auth: token-based login with ADMIN_SECRET env var
- Migrated sqlite3 → better-sqlite3
- database.js: async adapter (runAsync/allAsync/getAsync)
- purchaseService.js: lastID → lastInsertRowid
- userService.js: lastID → lastInsertRowid
- Removed sqlite3 from package.json
- Fixed: dotenv/config import added to index.js
- Fixed: ENCRYPTION_KEY validation (32+ char hex)
- Fixed: Dockerfile multi-stage build (no python needed)
- Fixed: Docker DNS (network: host in build)
- Fixed: docker-compose port 3001, healthcheck on 3001
- Added express, cookie-parser, pino-pretty, better-sqlite3 deps
4657b1dfb5