feat: 添加 LLM 连通性诊断脚本

用于排查 DashScope API 连接问题，直接打印 API Key、URL、
Model 配置和请求结果，不依赖 logging 配置。

运行: cd backend && python -m scripts.test_llm

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/scripts/test_llm.py

@@ -0,0 +1,78 @@
+"""LLM 连通性诊断脚本。
+直接运行：python -m backend.scripts.test_llm
+不依赖 logging 配置，所有输出直接 print。
+"""
+import json
+import sys
+from urllib import request, error
+
+sys.path.insert(0, ".")
+
+from backend.app.core.config import get_settings
+
+settings = get_settings()
+
+api_key = settings.llm_parse_api_key or settings.aliyun_ai_access_key_id
+api_url = settings.llm_parse_api_url
+model = settings.llm_parse_model
+
+print("=" * 60)
+print("LLM 连通性诊断")
+print("=" * 60)
+print(f"API URL:  {api_url}")
+print(f"Model:    {model}")
+print(f"API Key:  {api_key[:8]}...{api_key[-4:] if len(api_key) > 12 else '(太短或为空)'}")
+print(f"Key 来源: {'llm_parse_api_key' if settings.llm_parse_api_key else 'aliyun_ai_access_key_id (fallback)'}")
+print()
+
+if not api_key or api_key == "xxx":
+    print("[FATAL] API Key 未配置或为默认值 'xxx'！")
+    print("请在 .env 中设置 LLM_PARSE_API_KEY=sk-xxxxx")
+    sys.exit(1)
+
+payload = json.dumps({
+    "model": model,
+    "messages": [
+        {"role": "system", "content": "你是测试助手。只回复 JSON。"},
+        {"role": "user", "content": '请返回：{"status": "ok"}'},
+    ],
+    "temperature": 0.1,
+    "max_tokens": 64,
+}).encode("utf-8")
+
+headers = {
+    "Content-Type": "application/json",
+    "Authorization": f"Bearer {api_key}",
+}
+
+print("正在发送测试请求到 DashScope...")
+req = request.Request(url=api_url, data=payload, headers=headers, method="POST")
+
+try:
+    with request.urlopen(req, timeout=15) as resp:
+        body = resp.read().decode("utf-8")
+        result = json.loads(body)
+        print(f"[OK] HTTP {resp.status}")
+        print(f"完整响应:\n{json.dumps(result, indent=2, ensure_ascii=False)}")
+        content = result.get("choices", [{}])[0].get("message", {}).get("content", "")
+        print(f"\nLLM 回复内容: {content}")
+        print("\n[结论] LLM 连通正常！如果页面仍然失败，请检查服务器是否重启。")
+except error.HTTPError as exc:
+    body = exc.read().decode("utf-8", errors="ignore")
+    print(f"[FAIL] HTTP {exc.code}")
+    print(f"错误响应: {body}")
+    if exc.code == 401:
+        print("\n[结论] API Key 无效！请检查 LLM_PARSE_API_KEY 是否正确。")
+    elif exc.code == 403:
+        print("\n[结论] API Key 权限不足！请检查 DashScope 账户状态。")
+    elif exc.code == 429:
+        print("\n[结论] 请求频率超限！稍后重试。")
+    else:
+        print(f"\n[结论] HTTP 错误 {exc.code}，请检查 API 配置。")
+except error.URLError as exc:
+    print(f"[FAIL] 网络错误: {exc.reason}")
+    print("\n[结论] 无法连接到 DashScope，请检查网络。")
+except Exception as exc:
+    print(f"[FAIL] 未知错误: {type(exc).__name__}: {exc}")
+    import traceback
+    traceback.print_exc()