feat: enable unauthenticated server startup with runtime OAuth and update CI/CD to append Docker pull instructions to release notes

src/strava_mcp_server/strava_client.py

@@ -36,6 +36,9 @@ class StravaClient:
 
     async def get_valid_token(self) -> str:
         """Returns a valid access token, refreshing it if necessary."""
+        if not self.refresh_token:
+            raise ValueError("No Strava refresh token found. Please run the 'get_new_oauth_token' MCP tool to authenticate first.")
+            
         if not self.access_token or time.time() > self.expires_at - 60:
             await self._refresh_access_token()
         return self.access_token