feat: replace Directus with custom Node.js GraphQL backend

Removes Directus 11 and replaces it with a lean, purpose-built backend:
- packages/backend/: Fastify v5 + GraphQL Yoga v5 + Pothos (code-first)
  with Drizzle ORM, Redis sessions (session_token cookie), argon2 auth,
  Nodemailer, fluent-ffmpeg, and full gamification system ported from bundle
- Frontend: @directus/sdk replaced by graphql-request v7; services.ts fully
  rewritten with identical signatures; directus.ts now re-exports from api.ts
- Cookie renamed directus_session_token → session_token
- Dev proxy target updated 8055 → 4000
- compose.yml: Directus service removed, backend service added (port 4000)
- Dockerfile.backend: new multi-stage image with ffmpeg
- Dockerfile: bundle build step and ffmpeg removed from frontend image
- data-migration.ts: one-time script to migrate all Directus/sexy_ tables

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

packages/backend/src/graphql/builder.ts

@@ -0,0 +1,30 @@
+import SchemaBuilder from "@pothos/core";
+import ErrorsPlugin from "@pothos/plugin-errors";
+import type { DB } from "../db/connection.js";
+import type { SessionUser } from "../lib/auth.js";
+import type Redis from "ioredis";
+import { GraphQLDateTime, GraphQLJSON } from "graphql-scalars";
+
+export type Context = {
+  db: DB;
+  redis: InstanceType<typeof Redis>;
+  currentUser: SessionUser | null;
+  request: Request;
+  reply: unknown;
+};
+
+export const builder = new SchemaBuilder<{
+  Context: Context;
+  Scalars: {
+    DateTime: { Input: Date; Output: Date };
+    JSON: { Input: unknown; Output: unknown };
+  };
+}>({
+  plugins: [ErrorsPlugin],
+});
+
+builder.addScalarType("DateTime", GraphQLDateTime, {});
+builder.addScalarType("JSON", GraphQLJSON, {});
+
+builder.queryType({});
+builder.mutationType({});