fix: survive mumble disconnects without restarting audio stream

Guard stream_audio with _is_audio_ready() so that PCM frames are
dropped (not crashed on) when pymumble recreates SoundOutput with
encoder=None during reconnect. The ffmpeg pipeline stays alive,
position tracking remains accurate, and audio feeding resumes once
the codec is negotiated. Listeners hear brief silence instead of
a 30+ second restart with URL re-resolution.

Also adds chat messages to _auto_resume so users see what the bot
intends ("Resuming 'X' at M:SS in a moment" / "...aborted").

plugins/music.py

@@ -204,11 +204,24 @@ async def _auto_resume(bot) -> None:
     if data is None:
         return
 
+    elapsed = data.get("elapsed", 0.0)
+    title = _truncate(data.get("title", data["url"]))
+    pos = _fmt_time(elapsed)
+
     # Let pymumble fully stabilize after reconnect
     await asyncio.sleep(10)
 
     deadline = time.monotonic() + 60
     silence_needed = ps.get("duck_silence", 15)
+
+    ts = getattr(bot, "_last_voice_ts", 0.0)
+    if ts != 0.0 and time.monotonic() - ts < silence_needed:
+        await bot.send("0",
+                        f"Resuming '{title}' at {pos} once silent for "
+                        f"{silence_needed}s")
+    else:
+        await bot.send("0", f"Resuming '{title}' at {pos} in a moment")
+
     while time.monotonic() < deadline:
         await asyncio.sleep(2)
         ts = getattr(bot, "_last_voice_ts", 0.0)
@@ -218,6 +231,8 @@ async def _auto_resume(bot) -> None:
             break
     else:
         log.info("music: auto-resume aborted, channel not silent after 60s")
+        await bot.send("0", f"Resume of '{title}' aborted -- "
+                        "channel not silent")
         return
 
     # Re-check after waiting -- someone may have started playback manually