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/test_codex_models.py

@@ -133,7 +133,7 @@ def test_model_command_uses_runtime_access_token_for_codex_list(monkeypatch):
         captured["access_token"] = access_token
         return ["gpt-5.2-codex", "gpt-5.2"]
 
-    def _fake_prompt_model_selection(model_ids, current_model="", **_kwargs):
+    def _fake_prompt_model_selection(model_ids, current_model=""):
         captured["model_ids"] = list(model_ids)
         captured["current_model"] = current_model
         return None
@@ -181,7 +181,7 @@ def test_model_command_prompts_to_reuse_or_reauthenticate_codex_session(monkeypa
     )
     monkeypatch.setattr(
         "hermes_cli.auth._prompt_model_selection",
-        lambda model_ids, current_model="", **_kwargs: None,
+        lambda model_ids, current_model="": None,
     )
 
     _model_flow_openai_codex({}, current_model="gpt-5.4")
@@ -219,7 +219,7 @@ def test_model_command_uses_existing_codex_session_without_relogin(monkeypatch):
     )
     monkeypatch.setattr(
         "hermes_cli.auth._prompt_model_selection",
-        lambda model_ids, current_model="", **_kwargs: None,
+        lambda model_ids, current_model="": None,
     )
     monkeypatch.setattr(
         "hermes_cli.auth._login_openai_codex",