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/src/lib/gamification.ts

@@ -1,5 +1,5 @@
 import { eq, sql, and, gt, isNotNull, count, sum } from "drizzle-orm";
-import type { DB } from "../db/connection.js";
+import type { DB } from "../db/connection";
 import {
   user_points,
   user_stats,
@@ -9,7 +9,7 @@ import {
   user_achievements,
   achievements,
   users,
-} from "../db/schema/index.js";
+} from "../db/schema/index";
 
 export const POINT_VALUES = {
   RECORDING_CREATE: 50,