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>

Dockerfile

@@ -64,9 +64,6 @@ RUN pnpm --filter @sexy.pivoine.art/buttplug build
 # 3. Build frontend
 RUN pnpm --filter @sexy.pivoine.art/frontend build
 
-# 4. Build Directus bundle
-RUN pnpm --filter @sexy.pivoine.art/bundle build
-
 # Prune dev dependencies for production
 RUN pnpm install -rP
 
@@ -78,7 +75,6 @@ FROM node:22.11.0-slim AS runner
 # Install dumb-init for proper signal handling
 RUN apt-get update && apt-get install -y \
     dumb-init \
-    ffmpeg \
     && rm -rf /var/lib/apt/lists/*
 
 # Create non-root user
@@ -96,18 +92,13 @@ COPY --from=builder --chown=node:node /app/pnpm-lock.yaml ./pnpm-lock.yaml
 COPY --from=builder --chown=node:node /app/pnpm-workspace.yaml ./pnpm-workspace.yaml
 
 # Create package directories
-RUN mkdir -p packages/frontend packages/bundle packages/buttplug
+RUN mkdir -p packages/frontend packages/buttplug
 
 # Copy frontend artifacts
 COPY --from=builder --chown=node:node /app/packages/frontend/build ./packages/frontend/build
 COPY --from=builder --chown=node:node /app/packages/frontend/node_modules ./packages/frontend/node_modules
 COPY --from=builder --chown=node:node /app/packages/frontend/package.json ./packages/frontend/package.json
 
-# Copy bundle artifacts
-COPY --from=builder --chown=node:node /app/packages/bundle/dist ./packages/bundle/dist
-COPY --from=builder --chown=node:node /app/packages/bundle/node_modules ./packages/bundle/node_modules
-COPY --from=builder --chown=node:node /app/packages/bundle/package.json ./packages/bundle/package.json
-
 # Copy buttplug artifacts
 COPY --from=builder --chown=node:node /app/packages/buttplug/dist ./packages/buttplug/dist
 COPY --from=builder --chown=node:node /app/packages/buttplug/node_modules ./packages/buttplug/node_modules