Review fixes: correct Piper TTS API + bot env gating

Code review of the bridge/bot/docker work found:
- TTS bug: bridge called PiperVoice.synthesize(text, wav) but that method
  returns AudioChunks and takes a SynthesisConfig as its 2nd arg, not a wav
  file -> TTS would fail. Switched to synthesize_wav(text, wav_file).
  Verified: produces a valid 22050Hz mono WAV.
- run-bot.sh now waits if ANY of DISCORD_BOT_TOKEN/APP_ID/GUILD_ID is missing
  (config.ts throws on a missing one), preventing a supervisor crash-loop.

Verified clean: discord.js Events.ClientReady == 'clientReady' (existing
handler correct); image rebuilds.

bridge/server.py

@@ -197,7 +197,10 @@ def synthesize(text: str) -> Optional[bytes]:
         return None
     buf = io.BytesIO()
     with wave.open(buf, "wb") as wf:
-        _piper_voice.synthesize(text, wf)
+        # piper-tts API: synthesize_wav(text, wav_file) writes a full WAV;
+        # plain synthesize() returns AudioChunks and takes a SynthesisConfig
+        # (NOT a wav file) as its 2nd arg.
+        _piper_voice.synthesize_wav(text, wf)
     return buf.getvalue()