feat(voice): polish voice loop UX — filler kill, barge-in, DTX flush, time/RO TTS

End-to-end voice UX iteration after DAVE E2E shipped. Each change addresses a
real symptom Marius hit in live testing today:

- Kill the 3s filler ("mă gândesc"): Claude p50 is 4-7s so the filler always
  fired BEFORE the response and collided with it. Removed all filler infra
  from pipeline.py + tts_stream.py (FILLER_DELAY_S, _filler_task, push_filler,
  load_thinking_wav, thinking.wav cache).

- Barge-in: ttsq.clear() at the top of on_segment_done drops stale frames so
  a new utterance cuts off Echo's previous response cleanly.

- DTX silence flush: Discord stops sending RTP packets when the user goes
  silent (DTX), so the inline silence-check in sink.write() never fired for
  the trailing audio of an utterance — STT was missed entirely. Added a
  background poller thread that checks the silence-flush condition every
  200ms independent of incoming packets.

- Discord audio cadence fix: EchoStreamingAudioSource.read() blocked 100ms
  per call when pcm_queue was empty, wrecking Discord's 20ms frame pacing →
  client interpreted the stream as stutter and discarded leading frames
  (Marius heard "4 de minute în București" instead of the full sentence).
  Switched to get_frame_nowait() — instant return, silence frame on empty.

- RO time expansion: "23:09" was being read as "douăzeci și trei:nouă"
  with literal colon. Added expand_time() with feminine-correct minute
  formatting (un minut / două minute / douăzeci de minute / una de minute).

- Supertonic Unicode sanitize centralized in tools/tts.py: Romanian curly
  quotes (`„`, `"`, `"`, `—`, `…`) crash Supertonic with HTTP 500. Map them
  to ASCII at the synthesize() entry so BOTH voice mode and /audio command
  are covered without duplication. normalize.py re-exports for compat.

- Whisper offline: WhisperModel(..., local_files_only=True) — no more
  huggingface.co metadata GET on every startup. Model is already cached.

- Diagnostic logging across the chain: sink first-packet, VAD first-speech,
  voice stream block (Claude → callback), push_text (text → clauses queued),
  TTS pushed (clauses → frames). Lets future "spoke but Echo silent" bugs
  pinpoint exactly where the chain breaks.

- Captured Supertonic curly-quote lesson in tasks/lessons.md.

All 76 voice tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tools/tts.py

@@ -23,6 +23,24 @@ VOICES = {"M1", "M2", "M3", "M4", "M5", "F1", "F2", "F3", "F4", "F5"}
 DEFAULT_VOICE = "M2"
 DEFAULT_LANG = "ro"
 
+# Punctuation Supertonic synthesis rejects with HTTP 500 (Romanian curly quotes,
+# smart dashes, ellipsis, angle quotes). Mapped to ASCII so a stray „foo" in
+# any caller's text doesn't kill the whole request.
+_TTS_PUNCT_MAP = {
+    '„': '"', '“': '"', '”': '"',
+    '‘': "'", '’': "'", '‚': "'",
+    '«': '"', '»': '"',
+    '–': '-', '—': '-',
+    '…': '...',
+}
+
+
+def sanitize_for_supertonic(text: str) -> str:
+    """Replace Unicode punctuation Supertonic rejects with ASCII equivalents."""
+    for src, dst in _TTS_PUNCT_MAP.items():
+        text = text.replace(src, dst)
+    return text
+
 
 def synthesize(text: str, voice: str = DEFAULT_VOICE, lang: str = DEFAULT_LANG) -> dict:
     """Call Supertonic server and save audio to a temp WAV file.
@@ -34,6 +52,8 @@ def synthesize(text: str, voice: str = DEFAULT_VOICE, lang: str = DEFAULT_LANG)
     if not text or not text.strip():
         return {"ok": False, "error": "Text gol."}
 
+    text = sanitize_for_supertonic(text)
+
     voice = voice.upper()
     if voice not in VOICES:
         voice = DEFAULT_VOICE