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.

website/package.json

@@ -14,7 +14,7 @@
     "serve": "docusaurus serve",
     "write-translations": "docusaurus write-translations",
     "write-heading-ids": "docusaurus write-heading-ids",
-    "typecheck": "tsc -p . --noEmit",
+    "typecheck": "tsc",
     "lint:diagrams": "ascii-guard lint --exclude-code-blocks docs"
   },
   "dependencies": {
@@ -32,7 +32,7 @@
     "@docusaurus/module-type-aliases": "3.9.2",
     "@docusaurus/tsconfig": "3.9.2",
     "@docusaurus/types": "3.9.2",
-    "typescript": "^6.0.3"
+    "typescript": "~5.6.2"
   },
   "overrides": {
     "serialize-javascript": "^7.0.5",