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/resolvers/comments.ts

@@ -1,9 +1,9 @@
 import { GraphQLError } from "graphql";
-import { builder } from "../builder.js";
-import { CommentType } from "../types/index.js";
-import { comments, users } from "../../db/schema/index.js";
+import { builder } from "../builder";
+import { CommentType } from "../types/index";
+import { comments, users } from "../../db/schema/index";
 import { eq, and, desc } from "drizzle-orm";
-import { awardPoints, checkAchievements } from "../../lib/gamification.js";
+import { awardPoints, checkAchievements } from "../../lib/gamification";
 
 builder.queryField("commentsForVideo", (t) =>
   t.field({