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/test_web_server.py

@@ -1,16 +0,0 @@
-import uvicorn
-
-from hermes_cli import web_server
-
-
-def test_start_server_enables_ws_ping_for_half_open_detection(monkeypatch):
-    """WS ping must be configured so half-open connections (reverse-proxy 524,
-    dropped tunnels) raise WebSocketDisconnect into the reaping path (#32377)."""
-    captured = {}
-    monkeypatch.setattr(uvicorn, "run", lambda *args, **kwargs: captured.update(kwargs))
-
-    # Loopback bind => no auth gate, so this reaches uvicorn.run without setup.
-    web_server.start_server(host="127.0.0.1", port=0, open_browser=False)
-
-    assert captured["ws_ping_interval"] == 20.0
-    assert captured["ws_ping_timeout"] == 20.0