feat: add Postgres MCP integration for database testing

- Add postgres-mcp service to docker-compose.yml (SSE mode on port 8000)
- Add .mcp.json.example with SSE configuration template
- Add .gitignore entries for .claude/settings.local.json and .mcp.json
- Add MCP_EXAMPLES.md with query examples for testing scraping results
- Add analysis scripts: analyze-category-nulls.ts, check-product-details.ts,
  inspect-api-response.ts

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

docker-compose.yml

@@ -47,6 +47,19 @@ services:
       postgres:
         condition: service_healthy
 
+  postgres-mcp:
+    image: crystaldba/postgres-mcp:latest
+    container_name: supermarket-postgres-mcp
+    restart: unless-stopped
+    environment:
+      DATABASE_URI: postgresql://user:password@postgres:5432/supermarket
+    ports:
+      - "8000:8000"
+    command: ["--access-mode=unrestricted", "--transport=sse"]
+    depends_on:
+      postgres:
+        condition: service_healthy
+
 volumes:
   postgres_data:
   pgadmin_data: