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.

tests/hermes_cli/conftest.py

@@ -41,16 +41,6 @@ def _suppress_concurrent_hermes_gate(request, monkeypatch):
         from hermes_cli import main as _cli_main
     except Exception:
         return
-    # raising=False: under pytest's per-test spawn isolation, a concurrent
-    # xdist worker importing a module that transitively touches hermes_cli.main
-    # can briefly expose a partially-initialized module object here — one where
-    # _detect_concurrent_hermes_instances isn't defined yet. A bare setattr
-    # would raise AttributeError and error the (unrelated) test. The attribute
-    # always exists once main.py finishes importing, so a no-op when it's
-    # transiently absent is the correct, race-free default.
     monkeypatch.setattr(
-        _cli_main,
-        "_detect_concurrent_hermes_instances",
-        lambda *_a, **_k: [],
-        raising=False,
+        _cli_main, "_detect_concurrent_hermes_instances", lambda *_a, **_k: []
     )