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/transports/test_codex_app_server_session.py

@@ -196,40 +196,6 @@ class TestRunTurn:
         # turn_id propagated for downstream session-DB linkage
         assert r.turn_id == "turn-fake-001"
 
-    def test_token_usage_notification_is_captured(self):
-        client = FakeClient()
-        client.queue_notification(
-            "thread/tokenUsage/updated",
-            threadId="thread-fake-001",
-            turnId="turn-fake-001",
-            tokenUsage={
-                "last": {
-                    "totalTokens": 130,
-                    "inputTokens": 80,
-                    "cachedInputTokens": 20,
-                    "outputTokens": 25,
-                    "reasoningOutputTokens": 5,
-                },
-                "total": {
-                    "totalTokens": 500,
-                    "inputTokens": 300,
-                    "cachedInputTokens": 75,
-                    "outputTokens": 100,
-                    "reasoningOutputTokens": 25,
-                },
-                "modelContextWindow": 200000,
-            },
-        )
-        client.queue_notification(
-            "turn/completed",
-            threadId="t",
-            turn={"id": "tu1", "status": "completed", "error": None},
-        )
-        r = make_session(client).run_turn("hi", turn_timeout=2.0)
-        assert r.token_usage_last["totalTokens"] == 130
-        assert r.token_usage_total["totalTokens"] == 500
-        assert r.model_context_window == 200000
-
     def test_rich_content_turn_is_collapsed_to_text_payload(self):
         client = FakeClient()
         client.queue_notification(