feat: Phase 1 — Fastify backend with auth, users, admin API

Backend stack:
- Fastify v5 with JWT auth, CORS, cookies, rate limiting
- PostgreSQL via Drizzle ORM with full schema:
  users, presets, game_progress, shared_patches, likes, refresh_tokens
- Argon2 password hashing, httpOnly refresh cookie rotation

API endpoints:
- POST /api/v1/auth/register|login|refresh|logout
- GET|PATCH /api/v1/users/me (profile)
- GET /api/v1/admin/stats (dashboard KPIs)
- GET|PATCH /api/v1/admin/users (list, role change, ban)
- GET|PATCH /api/v1/admin/patches (moderation)
- GET /api/health

Infrastructure:
- Vite proxy /api → localhost:3001 for dev
- .env.example with all config vars
- Dockerfile updated: installs server deps, serves SPA + API
- npm run dev:server for backend hot-reload
- npm run db:push for schema sync

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/server/drizzle.config.js

@@ -0,0 +1,8 @@
+export default {
+  schema: './src/db/schema.js',
+  out: './src/db/migrations',
+  dialect: 'postgresql',
+  dbCredentials: {
+    url: process.env.DATABASE_URL || 'postgres://reaktor:reaktor_dev@localhost:5432/reaktor',
+  },
+};