feat: 浏览器一期：坐标点击 + live 截图

- browser_click_at(x, y)：视口坐标点击（1280x800、左上角
  原点），越界与非数字拒绝；live 视图里用户在截图上的
  点击落点就走这个工具。
- browser_live_shot：固定文件 browser-live.png + 状态
  sidecar browser-live.json（URL/标题/时间戳），watcher
  轮询一个稳定路径即可；技能要求每次动作后都调一次，
  保持画面最新。
- MCP 新增 browser_click_at / browser_live_shot 两个工具；
  技能补 live 视图一节；测试 9 项（含 fake mouse、越界、
  live 文件与状态读回）。

cloud/playwright_browser.py

@@ -148,6 +148,59 @@ class Browser:
         result["ok"] = True
         return result
 
+    def click_at(self, x, y):
+        """Click by viewport coordinates (CSS pixels, origin at the
+        top-left of the 1280x800 viewport). This is the tool the
+        console live view drives: the user clicks on a screenshot
+        and the coordinates arrive here. Bounds-checked so a
+        mis-scaled click cannot scroll the page into nowhere."""
+        try:
+            fx = float(x)
+            fy = float(y)
+        except (TypeError, ValueError):
+            raise BrowserError("click_at needs numeric x/y, got %r/%r"
+                               % (x, y))
+        if not (0 <= fx <= 1280 and 0 <= fy <= 800):
+            raise BrowserError(
+                "click_at out of viewport 1280x800: %s,%s" % (x, y))
+        self._ensure()
+        try:
+            self._page.mouse.click(fx, fy)
+            self._current_url = self._page.url
+        except Exception as exc:  # noqa: BLE001
+            raise BrowserError("click_at failed: %s" % exc)
+        result = self._info()
+        result["ok"] = True
+        result["x"] = fx
+        result["y"] = fy
+        return result
+
+    def live_shot(self, output_filename=None):
+        """Screenshot to a FIXED live-view file plus a JSON status
+        sidecar, so a watcher (console, user) can poll one stable
+        path instead of chasing per-shot filenames. The agent
+        should call this after every navigate/click/fill while a
+        live view is wanted. Returns path, bytes, url, title and
+        a unix timestamp."""
+        self._ensure()
+        name = _validate_basename(
+            output_filename or "browser-live.png", "output_filename")
+        path = os.path.join(self.cwd, name)
+        try:
+            self._page.screenshot(path=path)
+        except Exception as exc:  # noqa: BLE001
+            raise BrowserError("live_shot failed: %s" % exc)
+        info = self._info()
+        status = {"image": name, "path": path,
+                  "bytes": os.path.getsize(path),
+                  "url": info["url"], "title": info["title"],
+                  "timestamp": int(time.time())}
+        status_path = os.path.join(self.cwd, "browser-live.json")
+        with open(status_path, "w", encoding="utf-8") as fh:
+            json.dump(status, fh, ensure_ascii=False)
+        status["status_path"] = status_path
+        return status
+
     def evaluate(self, expression):
         if not expression or not str(expression).strip():
             raise BrowserError("expression is required")