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.

utils.py

@@ -355,44 +355,6 @@ def base_url_hostname(base_url: str) -> str:
     return (parsed.hostname or "").lower().rstrip(".")
 
 
-# ─── Model Capability Detection ──────────────────────────────────────────────
-
-
-def model_forces_max_completion_tokens(model: str) -> bool:
-    """Return True for model families that require ``max_completion_tokens``.
-
-    OpenAI's newer families reject ``max_tokens`` on /v1/chat/completions with
-    HTTP 400 ``unsupported_parameter`` — the caller must send
-    ``max_completion_tokens`` instead. This covers:
-
-    - ``gpt-4o`` / ``gpt-4o-mini`` / ``gpt-4o-*``
-    - ``gpt-4.1`` / ``gpt-4.1-*``
-    - ``gpt-5`` / ``gpt-5.x`` / ``gpt-5-*``
-    - ``o1`` / ``o1-*``
-    - ``o3`` / ``o3-*``
-    - ``o4`` / ``o4-*``
-
-    Handles vendor prefixes like ``openai/gpt-5.4`` by stripping to the tail.
-    The URL-based check (``base_url_hostname == "api.openai.com"``) misses
-    third-party OpenAI-compatible endpoints (custom OpenAI gateways,
-    OpenRouter) that front these models and enforce the same parameter
-    constraint, so name-based detection is required as a fallback.
-    """
-    m = (model or "").strip().lower()
-    if not m:
-        return False
-    if "/" in m:
-        m = m.rsplit("/", 1)[-1]
-    return (
-        m.startswith("gpt-4o")
-        or m.startswith("gpt-4.1")
-        or m.startswith("gpt-5")
-        or m.startswith("o1")
-        or m.startswith("o3")
-        or m.startswith("o4")
-    )
-
-
 def base_url_host_matches(base_url: str, domain: str) -> bool:
     """Return True when the base URL's hostname is ``domain`` or a subdomain.