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_status_bar.py

@@ -676,54 +676,3 @@ class TestStatusBarWidthSource:
         mock_get_app.assert_not_called()
         mock_shutil.assert_not_called()
         assert len(text) > 0
-
-
-class TestIdleSinceLastTurn:
-    """Time-since-last-final-agent-response read-out on the status bar."""
-
-    def test_hidden_before_first_turn(self):
-        assert HermesCLI._format_idle_since(None, turn_live=False) == ""
-
-    def test_hidden_while_turn_is_live(self):
-        assert HermesCLI._format_idle_since(time.time() - 30, turn_live=True) == ""
-
-    def test_shows_compact_idle_time_after_turn(self):
-        label = HermesCLI._format_idle_since(time.time() - 42, turn_live=False)
-        assert label.startswith("✓ ")
-        assert label == "✓ 42s"
-
-    def test_scales_to_minutes(self):
-        label = HermesCLI._format_idle_since(time.time() - 3 * 60, turn_live=False)
-        assert label == "✓ 3m"
-
-    def test_snapshot_carries_idle_since(self):
-        cli_obj = _make_cli()
-        cli_obj._last_turn_finished_at = time.time() - 10
-        cli_obj._prompt_start_time = None
-        cli_obj._prompt_duration = 5.0
-        snapshot = cli_obj._get_status_bar_snapshot()
-        assert snapshot["idle_since"].startswith("✓ ")
-
-    def test_snapshot_idle_empty_during_live_turn(self):
-        cli_obj = _make_cli()
-        cli_obj._last_turn_finished_at = time.time() - 10
-        cli_obj._prompt_start_time = time.time()
-        cli_obj._prompt_duration = 0.0
-        snapshot = cli_obj._get_status_bar_snapshot()
-        assert snapshot["idle_since"] == ""
-
-    def test_wide_status_bar_text_includes_idle(self):
-        cli_obj = _attach_agent(
-            _make_cli(),
-            prompt_tokens=10_230,
-            completion_tokens=2_220,
-            total_tokens=12_450,
-            api_calls=7,
-            context_tokens=12_450,
-            context_length=200_000,
-        )
-        cli_obj._last_turn_finished_at = time.time() - 42
-        cli_obj._prompt_start_time = None
-        cli_obj._prompt_duration = 7.0
-        text = cli_obj._build_status_bar_text(width=160)
-        assert "✓ 42s" in text