feat: 新增浏览器自动化插件 (browser_auto)

基于 Playwright 的无头浏览器操控，33 个操作：
- 连接: start/stop/status
- 导航: open/back/forward/reload/title/url
- 交互: click/fill/select/check/hover/press
- 提取: text/html/attr/value/eval/query
- 截图: screenshot (全页/元素)
- 等待: wait/wait-gone/wait-url
- 高级: pdf/cookies/set-cookie/viewport/download

测试: 101 个用例全部通过

tests/test_plugins.py

@@ -322,6 +322,37 @@ class TestTaskManager:
         assert "已清除" in result
 
 
+# ══════════════════════════════════════
+#  引擎加载测试
+# ══════════════════════════════════════
+
+class TestBrowserAuto:
+    """browser_auto 功能测试"""
+
+    @pytest.fixture
+    def browser(self):
+        mod = load_module("browser_auto", os.path.join(PLUGINS_DIR, "browser_auto.py"))
+        return mod.Plugin()
+
+    def test_status_stopped(self, browser):
+        result = browser.handle("status")
+        assert "未运行" in result
+
+    def test_invalid_operation(self, browser):
+        result = browser.handle("nonexistent")
+        assert "错误" in result
+
+    def test_empty_args(self, browser):
+        result = browser.handle("")
+        assert "错误" in result
+
+    def test_tool_info(self, browser):
+        info = browser.get_tool_info()
+        assert info["name"] == "browser_auto"
+        assert "浏览器" in info["description"]
+        assert len(info["keywords"]) > 0
+
+
 # ══════════════════════════════════════
 #  引擎加载测试
 # ══════════════════════════════════════