fix: switch backend to CommonJS, generate Drizzle migrations, add migrate script

- Remove "type": "module" and switch tsconfig to CommonJS/Node resolution
  to fix drizzle-kit ESM/CJS incompatibility
- Strip .js extensions from all backend TypeScript imports
- Fix gamification resolver: combine two .where() calls using and()
- Fix index.ts: wrap top-level awaits in async main(), fix Fastify+yoga
  request handling via handleNodeRequestAndResponse
- Generate initial Drizzle SQL migration (0000_pale_hellion.sql) for all
  15 tables
- Add src/scripts/migrate.ts: programmatic Drizzle migrator for production
- Copy migrations folder into Docker image (Dockerfile.backend)
- Add schema:migrate npm script

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/backend/package.json

@@ -1,7 +1,6 @@
 {
   "name": "@sexy.pivoine.art/backend",
   "version": "1.0.0",
-  "type": "module",
   "private": true,
   "scripts": {
     "dev": "tsx watch src/index.ts",
@@ -10,6 +9,7 @@
     "db:generate": "drizzle-kit generate",
     "db:migrate": "drizzle-kit migrate",
     "db:studio": "drizzle-kit studio",
+    "schema:migrate": "tsx src/scripts/migrate.ts",
     "migrate": "tsx src/scripts/data-migration.ts"
   },
   "dependencies": {