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/graphql/context.ts

@@ -1,8 +1,8 @@
 import type { YogaInitialContext } from "graphql-yoga";
-import type { Context } from "./builder.js";
-import { getSession } from "../lib/auth.js";
-import { db } from "../db/connection.js";
-import { redis } from "../lib/auth.js";
+import type { Context } from "./builder";
+import { getSession } from "../lib/auth";
+import { db } from "../db/connection";
+import { redis } from "../lib/auth";
 
 export async function buildContext(ctx: YogaInitialContext & { request: Request; reply: unknown; db: typeof db; redis: typeof redis }): Promise<Context> {
   const request = ctx.request;