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.

hermes_cli/plugins.py

@@ -1069,21 +1069,8 @@ class PluginManager:
             self._plugin_skills.clear()
             self._aux_tasks.clear()
             self._context_engine = None
-        # Set the flag up front as a re-entrancy guard (a plugin's register()
-        # can transitively trigger discovery again), but reset it if the sweep
-        # raises so a failed scan is NOT cached as "discovered with an empty
-        # registry" — callers swallow the exception and would otherwise be
-        # permanently stranded on the early-return above (the "No web provider
-        # configured" class of failures).
         self._discovered = True
-        try:
-            self._discover_and_load_inner()
-        except BaseException:
-            self._discovered = False
-            raise
 
-    def _discover_and_load_inner(self) -> None:
-        """The actual discovery sweep — see :meth:`discover_and_load`."""
         manifests: List[PluginManifest] = []
 
         # 1. Bundled plugins (<repo>/plugins/<name>/)