fix(agent): add missing ping() to OllamaBackend and OdooClient

Health endpoint called .ping() on both but neither implemented it,
causing ollama/odoo to always show as error and the bot to stay offline.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agent_service/tools/odoo_client.py

@@ -55,6 +55,10 @@ class OdooClient:
         self._models = xmlrpc.client.ServerProxy(
             f'{self._url}/xmlrpc/2/object', transport=transport, allow_none=True)
 
+    async def ping(self) -> None:
+        """Raise if Odoo is unreachable."""
+        await self._xmlrpc_call(self._common, 'version')
+
     async def connect(self):
         await self._authenticate()
         if self._pg_dsn: