add api key settings and agent docs

README.md

@@ -29,6 +29,23 @@ The UI runs on port `3000`. The HTTP API runs separately on port `3002`.
 3. Check the API:
    `http://localhost:3002/api/health`
 
+You can change the server API key without restarting:
+
+```bash
+curl -X POST http://localhost:3002/api/config/api-key \
+  -H "Content-Type: application/json" \
+  -d "{\"apiKey\":\"YOUR_GEMINI_API_KEY\",\"persist\":true}"
+```
+
+You can also pass a temporary Gemini key for one call:
+
+```bash
+curl -X POST http://localhost:3002/api/generate \
+  -H "Content-Type: application/json" \
+  -H "x-gemini-api-key: YOUR_GEMINI_API_KEY" \
+  -d "{\"prompt\":\"Create a clean product poster\"}"
+```
+
 ### API examples
 
 Generate or edit with JSON/base64:
@@ -58,3 +75,5 @@ curl -X POST http://localhost:3002/api/analyze-document \
 ```
 
 Optional API auth: set `API_AUTH_TOKEN`, then send either `Authorization: Bearer <token>` or `x-api-key: <token>`.
+
+For Agent-facing image editing instructions, see `API图片修改-Agent.md`.