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/db/schema/articles.ts

@@ -0,0 +1,37 @@
+import {
+  pgTable,
+  text,
+  timestamp,
+  boolean,
+  index,
+  uniqueIndex,
+} from "drizzle-orm/pg-core";
+import { users } from "./users.js";
+import { files } from "./files.js";
+
+export const articles = pgTable(
+  "articles",
+  {
+    id: text("id").primaryKey().$defaultFn(() => crypto.randomUUID()),
+    slug: text("slug").notNull(),
+    title: text("title").notNull(),
+    excerpt: text("excerpt"),
+    content: text("content"),
+    image: text("image").references(() => files.id, { onDelete: "set null" }),
+    tags: text("tags").array().default([]),
+    publish_date: timestamp("publish_date").notNull().defaultNow(),
+    author: text("author").references(() => users.id, { onDelete: "set null" }),
+    category: text("category"),
+    featured: boolean("featured").default(false),
+    date_created: timestamp("date_created").notNull().defaultNow(),
+    date_updated: timestamp("date_updated"),
+  },
+  (t) => [
+    uniqueIndex("articles_slug_idx").on(t.slug),
+    index("articles_publish_date_idx").on(t.publish_date),
+    index("articles_featured_idx").on(t.featured),
+  ],
+);
+
+export type Article = typeof articles.$inferSelect;
+export type NewArticle = typeof articles.$inferInsert;