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/resolvers/stats.ts

@@ -0,0 +1,29 @@
+import { builder } from "../builder.js";
+import { StatsType } from "../types/index.js";
+import { users, videos } from "../../db/schema/index.js";
+import { eq, count } from "drizzle-orm";
+
+builder.queryField("stats", (t) =>
+  t.field({
+    type: StatsType,
+    resolve: async (_root, _args, ctx) => {
+      const modelsCount = await ctx.db
+        .select({ count: count() })
+        .from(users)
+        .where(eq(users.role, "model"));
+      const viewersCount = await ctx.db
+        .select({ count: count() })
+        .from(users)
+        .where(eq(users.role, "viewer"));
+      const videosCount = await ctx.db
+        .select({ count: count() })
+        .from(videos);
+
+      return {
+        models_count: modelsCount[0]?.count || 0,
+        viewers_count: viewersCount[0]?.count || 0,
+        videos_count: videosCount[0]?.count || 0,
+      };
+    },
+  }),
+);