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>

docker-compose.yml

@@ -1,31 +1,16 @@
 services:
-  postgres:
-    image: postgres:16-alpine
-    environment:
-      POSTGRES_USER: ${DB_USER:-pamietnik}
-      POSTGRES_PASSWORD: ${DB_PASSWORD:?DB_PASSWORD is required}
-      POSTGRES_DB: ${DB_NAME:-pamietnik}
-    volumes:
-      - pgdata:/var/lib/postgresql/data
-    healthcheck:
-      test: ["CMD-SHELL", "pg_isready -U ${DB_USER:-pamietnik}"]
-      interval: 5s
-      timeout: 5s
-      retries: 5
-
   api:
     build:
       context: .
       dockerfile: Dockerfile
     ports:
-      - "9050:8080"
+      - "${APP_PORT:-9050}:8080"
+    extra_hosts:
+      - "host-gateway:host-gateway"
     environment:
-      DATABASE_URL: postgres://${DB_USER:-pamietnik}:${DB_PASSWORD:?DB_PASSWORD is required}@postgres:5432/${DB_NAME:-pamietnik}?sslmode=disable
+      DATABASE_URL: postgres://${DB_USER:-pamietnik}:${DB_PASSWORD:?DB_PASSWORD is required}@host-gateway:5433/${DB_NAME:-pamietnik}?sslmode=disable
       LISTEN_ADDR: :8080
-    depends_on:
-      postgres:
-        condition: service_healthy
+      UPLOAD_DIR: /uploads
+    volumes:
+      - /volume2/docker/pamietnik/uploads:/uploads
     restart: unless-stopped
-
-volumes:
-  pgdata: