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/frontend/src/routes/leaderboard/+page.server.ts

@@ -1,5 +1,17 @@
 import { redirect } from "@sveltejs/kit";
 import type { PageServerLoad } from "./$types";
+import { gql } from "graphql-request";
+import { getGraphQLClient } from "$lib/api";
+
+const LEADERBOARD_QUERY = gql`
+  query Leaderboard($limit: Int, $offset: Int) {
+    leaderboard(limit: $limit, offset: $offset) {
+      user_id display_name avatar
+      total_weighted_points total_raw_points
+      recordings_count playbacks_count achievements_count rank
+    }
+  }
+`;
 
 export const load: PageServerLoad = async ({ fetch, url, locals }) => {
 	// Guard: Redirect to login if not authenticated
@@ -11,22 +23,27 @@ export const load: PageServerLoad = async ({ fetch, url, locals }) => {
 		const limit = parseInt(url.searchParams.get("limit") || "100");
 		const offset = parseInt(url.searchParams.get("offset") || "0");
 
-		const response = await fetch(
-			`/api/sexy/gamification/leaderboard?limit=${limit}&offset=${offset}`,
-		);
-
-		if (!response.ok) {
-			throw new Error("Failed to fetch leaderboard");
-		}
-
-		const data = await response.json();
+		const client = getGraphQLClient(fetch);
+		const data = await client.request<{
+			leaderboard: {
+				user_id: string;
+				display_name: string | null;
+				avatar: string | null;
+				total_weighted_points: number | null;
+				total_raw_points: number | null;
+				recordings_count: number | null;
+				playbacks_count: number | null;
+				achievements_count: number | null;
+				rank: number;
+			}[];
+		}>(LEADERBOARD_QUERY, { limit, offset });
 
 		return {
-			leaderboard: data.data || [],
+			leaderboard: data.leaderboard || [],
 			pagination: {
 				limit,
 				offset,
-				hasMore: data.data?.length === limit,
+				hasMore: data.leaderboard?.length === limit,
 			},
 		};
 	} catch (error) {