fix: avoid Discord /tts conflict

docs/tools/slash-commands.md

@@ -68,6 +68,7 @@ Text + native (when enabled):
 - `/debug show|set|unset|reset` (runtime overrides, owner-only; requires `commands.debug: true`)
 - `/usage off|tokens|full|cost` (per-response usage footer or local cost summary)
 - `/tts on|off|status|provider|limit|summary|audio` (control TTS; see [/tts](/tts))
+  - Discord: native command is `/voice` (Discord reserves `/tts`); text `/tts` still works.
 - `/stop`
 - `/restart`
 - `/dock-telegram` (alias: `/dock_telegram`) (switch replies to Telegram)