fix: flip audio default to file (backward compat)

- Default: sendAudio (file with metadata) - preserves old behavior
- Opt-in: [[audio_as_voice]] tag for voice bubble

This is non-breaking - existing integrations keep working.

src/telegram/bot.ts

@@ -1250,12 +1250,14 @@ async function deliverReplies(params: {
           ...mediaParams,
         });
       } else if (kind === "audio") {
-        const useVoice = reply.audioAsVoice === true; // default false
+        const useVoice = reply.audioAsVoice === true; // default false (backward compatible)
         if (useVoice) {
+          // Voice message - displays as round playable bubble (opt-in via [[audio_as_voice]])
           await bot.api.sendVoice(chatId, file, {
             ...mediaParams,
           });
         } else {
+          // Audio file - displays with metadata (title, duration) - DEFAULT
           await bot.api.sendAudio(chatId, file, {
             ...mediaParams,
           });