feat(web): send honest nanobot UA for Keenable

Keenable is a first-party API, so identify as nanobot/<version> instead
of the shared spoofed-browser User-Agent used by scraping providers.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nanobot/agent/tools/web.py

@@ -489,8 +489,10 @@ class WebSearchTool(Tool):
             return f"Error: {e}"
 
     async def _search_keenable(self, query: str, n: int) -> str:
+        from nanobot import __version__
         api_key = self.config.api_key or os.environ.get("KEENABLE_API_KEY", "")
-        headers = {"Content-Type": "application/json", "User-Agent": self.user_agent}
+        # First-party API: identify honestly instead of the spoofed browser UA.
+        headers = {"Content-Type": "application/json", "User-Agent": f"nanobot/{__version__}"}
         if api_key:
             headers["X-API-Key"] = api_key
         try: