fix: YouTube JS runtime check, Douyin health check, cli bare except, config permission race (#104)

- YouTube: warn when only Node.js is installed but yt-dlp config file
  is missing (previously returned "ok" incorrectly)
- Douyin: use `mcporter list` instead of calling with a hardcoded
  invalid share URL that always fails
- cli: replace bare `except:` with `except Exception:` in
  `_detect_environment` to avoid catching KeyboardInterrupt/SystemExit
- cli: fix unclosed file handle for cloud VM detection
- config: use `os.open()` with 0o600 mode to eliminate permission
  race window when saving credentials

agent_reach/channels/douyin.py

@@ -42,13 +42,15 @@ class DouyinChannel(Channel):
                 )
         except Exception:
             return "off", "mcporter 连接异常"
+        # Verify MCP connectivity by listing available tools instead of
+        # calling with a hardcoded (invalid) share link that always fails.
         try:
             r = subprocess.run(
-                [mcporter, "call", "douyin.parse_douyin_video_info(share_link: \"https://www.douyin.com\")"],
+                [mcporter, "list", "douyin"],
                 capture_output=True, encoding="utf-8", errors="replace", timeout=15
             )
-            if r.returncode == 0:
+            if r.returncode == 0 and r.stdout.strip():
                 return "ok", "完整可用（视频解析、下载链接获取）"
-            return "warn", "MCP 已连接但调用异常，检查 douyin-mcp-server 服务是否在运行"
+            return "warn", "MCP 已连接但工具列表为空，检查 douyin-mcp-server 服务是否在运行"
         except Exception:
             return "warn", "MCP 连接异常，检查 douyin-mcp-server 服务是否在运行"