Add Gitea CI/CD pipeline and shared infra setup

- docker-compose.yml: remove bundled postgres, connect to shared
  postgres via host-gateway:5433, add uploads volume, configurable port
- .gitea/workflows/deploy.yml: Gitea Actions workflow for automated
  deploy on push to main
- infra/README.md: step-by-step setup guide for NAS deployment
  (shared postgres, pgAdmin, act_runner, Gitea secrets)

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

.gitea/workflows/deploy.yml

@@ -0,0 +1,26 @@
+name: Deploy to NAS
+
+on:
+  push:
+    branches: [main]
+
+jobs:
+  deploy:
+    runs-on: self-hosted
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Write .env
+        run: printf 'DB_PASSWORD=%s\n' '${{ secrets.DB_PASSWORD }}' > ${{ secrets.DEPLOY_DIR }}/.env
+
+      - name: Build & Deploy
+        run: |
+          cp -r ${{ github.workspace }}/. ${{ secrets.DEPLOY_DIR }}/
+          docker compose -f ${{ secrets.DEPLOY_DIR }}/docker-compose.yml up --build -d
+
+      - name: Health check
+        run: |
+          sleep 15
+          curl -sf http://localhost:9050/healthz || exit 1