opentui(phase3): launcher integration — HERMES_TUI_ENGINE dual-engine

hermes --tui launches the native OpenTUI engine (Bun) when
HERMES_TUI_ENGINE=opentui (env) or display.tui_engine=opentui (config);
Ink stays the default and the shipping path is untouched.

- _resolve_tui_engine() (env > config > ink); refuses opentui on
  Windows/Termux (no Bun) -> falls back to ink with a notice.
- _make_opentui_argv() -> [bun, src/entry.real.tsx] (no build step).
- _bun_bin() with HERMES_BUN override.
- Branch at top of _make_tui_argv BEFORE _ensure_tui_node (Bun-only host
  must not bootstrap Node).
- Gate _launch_tui NODE_OPTIONS/--max-old-space-size on engine==ink (Bun
  is JSC; the V8 flag errors/ignores).

Verified end-to-end via tmux: real hermes --tui -> Bun -> OpenTUI ->
real Python gateway streamed a real reply. No-flag default still ink.

tools/voice_mode.py

@@ -75,7 +75,6 @@ def _termux_api_app_installed() -> bool:
             text=True,
             timeout=5,
             check=False,
-            stdin=subprocess.DEVNULL,
         )
         return "package:com.termux.api" in (result.stdout or "")
     except Exception:
@@ -389,7 +388,7 @@ class TermuxAudioRecorder:
             "-c", str(CHANNELS),
         ]
         try:
-            subprocess.run(command, capture_output=True, text=True, timeout=15, check=True, stdin=subprocess.DEVNULL)
+            subprocess.run(command, capture_output=True, text=True, timeout=15, check=True)
         except subprocess.CalledProcessError as e:
             details = (e.stderr or e.stdout or str(e)).strip()
             raise RuntimeError(f"Termux microphone start failed: {details}") from e
@@ -406,7 +405,7 @@ class TermuxAudioRecorder:
         mic_cmd = _termux_microphone_command()
         if not mic_cmd:
             return
-        subprocess.run([mic_cmd, "-q"], capture_output=True, text=True, timeout=15, check=False, stdin=subprocess.DEVNULL)
+        subprocess.run([mic_cmd, "-q"], capture_output=True, text=True, timeout=15, check=False)
 
     def stop(self) -> Optional[str]:
         with self._lock:
@@ -1096,7 +1095,7 @@ def play_audio_file(file_path: str) -> bool:
         exe = shutil.which(cmd[0])
         if exe:
             try:
-                proc = subprocess.Popen(cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, stdin=subprocess.DEVNULL)
+                proc = subprocess.Popen(cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
                 with _playback_lock:
                     _active_playback = proc
                 proc.wait(timeout=300)