Add local-first SPA architecture and containerized production deploy.

Move data access to use-cases and IndexedDB repositories with optional
remote fallback, changelog/sync ports, and encrypted local backup.
Add production Docker Compose (nginx frontend + optional backend) and
Apache host proxy configuration for deployment.

Co-authored-by: Cursor <cursoragent@cursor.com>

docker-compose.prod.yml

@@ -0,0 +1,32 @@
+services:
+  frontend:
+    build:
+      context: ./frontend
+      dockerfile: Dockerfile.prod
+      args:
+        VITE_DATA_MODE: ${VITE_DATA_MODE:-local}
+    container_name: sg_frontend
+    ports:
+      - "${FRONTEND_BIND:-127.0.0.1}:${FRONTEND_PORT:-8080}:80"
+    restart: unless-stopped
+
+  backend:
+    profiles: ["with-backend"]
+    build:
+      context: ./backend
+      dockerfile: Dockerfile.prod
+    container_name: sg_backend
+    environment:
+      DJANGO_SETTINGS_MODULE: config.settings
+      SECRET_KEY: ${DJANGO_SECRET_KEY:-change-me-in-production}
+      DEBUG: "False"
+      ALLOWED_HOSTS: ${ALLOWED_HOSTS:-localhost,127.0.0.1}
+      DATABASE_PATH: /app/data/db.sqlite3
+    volumes:
+      - sqlite_data:/app/data
+    ports:
+      - "${BACKEND_BIND:-127.0.0.1}:${BACKEND_PORT:-8000}:8000"
+    restart: unless-stopped
+
+volumes:
+  sqlite_data: