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/cli/test_cli_browser_connect.py

@@ -238,7 +238,7 @@ class TestChromeDebugLaunch:
         cli._pending_input = Queue()
         monkeypatch.delenv("BROWSER_CDP_URL", raising=False)
 
-        with patch("hermes_cli.cli_commands_mixin.is_browser_debug_ready", return_value=True), \
+        with patch("cli.is_browser_debug_ready", return_value=True), \
              patch("tools.browser_tool.cleanup_all_browsers"), \
              patch("tools.browser_tool._ensure_cdp_supervisor"), \
              redirect_stdout(StringIO()):