fix(gateway): replace assertions with proper error handling in Telegram and Feishu

Python assertions are stripped when running with `python -O` (optimized
mode), making them unsuitable for runtime error handling.

1. `telegram_network.py:113` — After exhausting all fallback IPs, the code
   uses `assert last_error is not None` before `raise last_error`. In
   optimized mode, the assert is skipped; if `last_error` is unexpectedly
   None, `raise None` produces a confusing `TypeError` instead of a
   meaningful error. Replace with an explicit `if` check that raises
   `RuntimeError` with a descriptive message.

2. `feishu.py:975` — The `_configure_with_overrides` closure uses
   `assert original_configure is not None` as a guard. While the outer
   scope only installs this closure when `original_configure` is not None,
   the assert would silently disappear in optimized mode. Replace with an
   explicit `if` check for defensive safety.

gateway/platforms/feishu.py

@@ -973,7 +973,8 @@ def _run_official_feishu_ws_client(ws_client: Any, adapter: Any) -> None:
         return await original_connect(*args, **kwargs)
 
     def _configure_with_overrides(conf: Any) -> Any:
-        assert original_configure is not None
+        if original_configure is None:
+            raise RuntimeError("Feishu _configure_with_overrides called but original_configure is None")
         result = original_configure(conf)
         _apply_runtime_ws_overrides()
         return result

gateway/platforms/telegram_network.py

@@ -110,7 +110,8 @@ class TelegramFallbackTransport(httpx.AsyncBaseTransport):
                 logger.warning("[Telegram] Fallback IP %s failed: %s", ip, exc)
                 continue
 
-        assert last_error is not None
+        if last_error is None:
+            raise RuntimeError("All Telegram fallback IPs exhausted but no error was recorded")
         raise last_error
 
     async def aclose(self) -> None: