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.

agent/system_prompt.py

@@ -191,23 +191,9 @@ def build_system_prompt_parts(agent: Any, system_message: Optional[str] = None)
             )
             if toolset
         }
-        # Focus mode (opt-in) demotes non-coding skill categories to
-        # names-only in the index (never hidden — skill_view/skills_list
-        # reach everything, and every name stays visible for recall). The
-        # default coding posture leaves the index untouched.
-        _compact_cats = frozenset()
-        try:
-            from agent.coding_context import coding_compact_skill_categories
-
-            _compact_cats = coding_compact_skill_categories(
-                platform=agent.platform, cwd=resolve_context_cwd()
-            )
-        except Exception:
-            _compact_cats = frozenset()
         skills_prompt = _r.build_skills_system_prompt(
             available_tools=agent.valid_tool_names,
             available_toolsets=avail_toolsets,
-            compact_categories=_compact_cats or None,
         )
     else:
         skills_prompt = ""
@@ -235,26 +221,6 @@ def build_system_prompt_parts(agent: Any, system_message: Optional[str] = None)
     if _env_hints:
         stable_parts.append(_env_hints)
 
-    # Coding posture (base Hermes, any interactive coding surface in a code
-    # workspace — see agent/coding_context.py). The operating brief + the live
-    # git/workspace snapshot are built once here and cached for the session;
-    # the snapshot is never re-probed per turn (that would break the prompt
-    # cache), so the brief tells the model to re-check git before relying on it.
-    if agent.valid_tool_names:
-        try:
-            from agent.coding_context import coding_system_blocks
-
-            stable_parts.extend(
-                coding_system_blocks(
-                    platform=agent.platform,
-                    cwd=resolve_context_cwd(),
-                    model=agent.model,
-                )
-            )
-        except Exception:
-            # Coding-context probing must never block prompt build.
-            pass
-
     # Local Python toolchain probe — names python/pip/uv/PEP-668 state when
     # something is non-default so the model can pick the right install
     # strategy without discovering by failure.  Emits a single line; emits