fix: address PR review round 5 — streaming guard, VC auth, history prefix, auto-TTS control

1. Gate _streaming_api_call to chat_completions mode only — Anthropic and
   Codex fall back to _interruptible_api_call. Preserve Anthropic base_url
   across all client rebuild paths (interrupt, fallback, 401 refresh).

2. Discord VC synthetic events now use chat_type="channel" instead of
   defaulting to "dm" — prevents session bleed into DM context.
   Authorization runs before echoing transcript. Sanitize @everyone/@here
   in voice transcripts.

3. CLI voice prefix ("[Voice input...]") is now API-call-local only —
   stripped from returned history so it never persists to session DB or
   resumed sessions.

4. /voice off now disables base adapter auto-TTS via _auto_tts_disabled_chats
   set — voice input no longer triggers TTS when voice mode is off.

gateway/platforms/base.py

@@ -351,6 +351,8 @@ class BasePlatformAdapter(ABC):
         # Key: session_key (e.g., chat_id), Value: (event, asyncio.Event for interrupt)
         self._active_sessions: Dict[str, asyncio.Event] = {}
         self._pending_messages: Dict[str, MessageEvent] = {}
+        # Chats where auto-TTS on voice input is disabled (set by /voice off)
+        self._auto_tts_disabled_chats: set = set()
     
     @property
     def name(self) -> str:
@@ -733,8 +735,12 @@ class BasePlatformAdapter(ABC):
                     logger.info("[%s] extract_images found %d image(s) in response (%d chars)", self.name, len(images), len(response))
                 
                 # Auto-TTS: if voice message, generate audio FIRST (before sending text)
+                # Skipped when the chat has voice mode disabled (/voice off)
                 _tts_path = None
-                if event.message_type == MessageType.VOICE and text_content and not media_files:
+                if (event.message_type == MessageType.VOICE
+                        and text_content
+                        and not media_files
+                        and event.source.chat_id not in self._auto_tts_disabled_chats):
                     try:
                         from tools.tts_tool import text_to_speech_tool, check_tts_requirements
                         if check_tts_requirements():