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.

plugins/video_gen/fal/__init__.py

@@ -291,7 +291,6 @@ def _build_payload(
 # ---------------------------------------------------------------------------
 
 _fal_client: Any = None
-_fal_client_lock = threading.Lock()
 
 
 def _load_fal_client() -> Any:
@@ -299,19 +298,13 @@ def _load_fal_client() -> Any:
 
     Delegates the actual import to :func:`tools.fal_common.import_fal_client`
     so the ``lazy_deps`` ensure-install handling stays in one place.
-
-    Thread-safe via double-checked locking: concurrent first calls import
-    the SDK exactly once instead of each racing thread re-running the import.
     """
     global _fal_client
     if _fal_client is not None:
         return _fal_client
-    with _fal_client_lock:
-        if _fal_client is not None:  # re-check inside the lock
-            return _fal_client
-        from tools.fal_common import import_fal_client
-        _fal_client = import_fal_client()
-        return _fal_client
+    from tools.fal_common import import_fal_client
+    _fal_client = import_fal_client()
+    return _fal_client
 
 
 # ---------------------------------------------------------------------------