fix(gateway): STT config resolution, stream consumer flood control fallback

Three targeted fixes from user-reported issues:

1. STT config resolution (transcription_tools.py):
   _has_openai_audio_backend() and _resolve_openai_audio_client_config()
   now check stt.openai.api_key/base_url in config.yaml FIRST, before
   falling back to env vars. Fixes voice transcription breaking when
   using a custom OpenAI-compatible endpoint via config.yaml.

2. Stream consumer flood control fallback (stream_consumer.py):
   When an edit fails mid-stream (e.g., Telegram flood control returns
   failure for waits >5s), reset _already_sent to False so the normal
   final send path delivers the complete response. Previously, a
   truncated partial was left as the final message.

3. Telegram edit_message comment alignment (telegram.py):
   Clarify that long flood waits return failure so streaming can fall
   back to a normal final send.

gateway/platforms/telegram.py

@@ -901,9 +901,8 @@ class TelegramAdapter(BasePlatformAdapter):
                     pass  # best-effort truncation
                 return SendResult(success=True, message_id=message_id)
             # Flood control / RetryAfter — short waits are retried inline,
-            # long waits (>5s) return a failure so the caller can decide
-            # whether to wait or degrade gracefully.  (grammY auto-retry
-            # pattern: maxDelaySeconds threshold.)
+            # long waits return a failure immediately so streaming can fall back
+            # to a normal final send instead of leaving a truncated partial.
             retry_after = getattr(e, "retry_after", None)
             if retry_after is not None or "retry after" in err_str:
                 wait = retry_after if retry_after else 1.0
@@ -912,12 +911,7 @@ class TelegramAdapter(BasePlatformAdapter):
                     self.name, wait,
                 )
                 if wait > 5.0:
-                    # Long wait — return failure immediately so callers
-                    # (progress edits, stream consumer) aren't blocked.
-                    return SendResult(
-                        success=False,
-                        error=f"flood_control:{wait}",
-                    )
+                    return SendResult(success=False, error=f"flood_control:{wait}")
                 await asyncio.sleep(wait)
                 try:
                     await self._bot.edit_message_text(