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.

hermes_cli/service_manager.py

@@ -739,55 +739,13 @@ class S6ServiceManager:
         """
         self._run_svc("-u", "start", name)
 
-    def _supervised_pid(self, name: str) -> int | None:
-        """Return the PID of the supervised gateway process, or None.
-
-        Parses ``s6-svstat`` output (``up (pid NNNN) ...``). Used to
-        mark an operator-initiated stop with the planned-stop marker so
-        the gateway's shutdown handler classifies the incoming SIGTERM
-        as intentional rather than an unexpected kill (issue #42675).
-        Best-effort: any parse/exec failure returns None.
-        """
-        import subprocess
-
-        try:
-            result = subprocess.run(
-                [f"{_S6_BIN_DIR}/s6-svstat", str(self.scandir / name)],
-                capture_output=True, text=True, timeout=5,
-            )
-        except (OSError, subprocess.SubprocessError):
-            return None
-        if result.returncode != 0:
-            return None
-        m = re.search(r"\(pid (\d+)\)", result.stdout)
-        return int(m.group(1)) if m else None
-
     def stop(self, name: str) -> None:
         """Bring down a registered service (``s6-svc -d``).
 
-        Writes a planned-stop marker naming the supervised gateway PID
-        BEFORE sending the down command, so the gateway's shutdown
-        handler recognises this SIGTERM as an operator-initiated stop
-        and persists ``gateway_state=stopped`` (respecting the explicit
-        intent). Without the marker, an intentional ``hermes gateway
-        stop`` is indistinguishable from the container/s6 SIGTERM sent on
-        ``docker restart``; the latter must NOT persist ``stopped`` or
-        container_boot refuses to auto-start on the next boot (#42675).
-        The marker write is best-effort — a failure only means the stop
-        is treated as signal-initiated, which is the safe fallback.
-
         Raises:
             GatewayNotRegisteredError: no service directory for ``name``.
             S6CommandError: s6-svc exited non-zero for any other reason.
         """
-        pid = self._supervised_pid(name)
-        if pid is not None:
-            try:
-                from gateway.status import write_planned_stop_marker
-
-                write_planned_stop_marker(pid)
-            except Exception:
-                pass
         self._run_svc("-d", "stop", name)
 
     def restart(self, name: str) -> None: