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/hermes_cli/test_banner.py

@@ -167,36 +167,3 @@ def test_build_welcome_banner_disabled_mcp_shows_disabled_not_failed():
     assert "broken" in output
     assert "failed" in output
 
-
-def test_build_welcome_banner_configured_mcp_is_not_failed():
-    """A configured MCP server with no connection attempt yet is not a failure."""
-    with (
-        patch.object(model_tools, "check_tool_availability", return_value=(["web"], [])),
-        patch.object(banner, "get_available_skills", return_value={}),
-        patch.object(banner, "get_update_result", return_value=None),
-        patch.object(
-            tools.mcp_tool,
-            "get_mcp_status",
-            return_value=[
-                {
-                    "name": "docker-profile",
-                    "transport": "stdio",
-                    "tools": 0,
-                    "connected": False,
-                    "disabled": False,
-                    "status": "configured",
-                },
-            ],
-        ),
-    ):
-        console = Console(record=True, force_terminal=False, color_system=None, width=160)
-        banner.build_welcome_banner(
-            console=console, model="anthropic/test-model", cwd="/tmp/project",
-            tools=[{"function": {"name": "read_file"}}],
-            get_toolset_for_tool=lambda n: "file",
-        )
-
-    output = console.export_text()
-    assert "docker-profile" in output
-    assert "configured" in output
-    assert "failed" not in output