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/agent/test_curator.py

@@ -668,8 +668,8 @@ def test_state_atomic_write_no_tmp_leftovers(curator_env):
     c = curator_env["curator"]
     c.save_state({"paused": True})
     parent = c._state_file().parent
-    tmp_files = [p.name for p in parent.iterdir() if p.name.endswith(".tmp")]
-    assert tmp_files == []
+    for p in parent.iterdir():
+        assert not p.name.startswith(".curator_state_"), f"tmp leftover: {p.name}"
 
 
 def test_state_preserves_last_report_path(curator_env):