feat: add shell_exec tool and fix orchestrator model name resolution

- Add shell_exec to orchestrator tool suite (system.py + __init__.py)
  Runs arbitrary shell commands on the Cortex host with timeout (1–120s),
  combined stdout/stderr output, optional working_dir, and exit code reporting.
  Enables system diagnostics (df, ls, ps, journalctl, etc.) from Agent mode.

- Fix orchestrator_engine.run() to use model_name from resolved registry entry
  Previously used settings.orchestrator_model (.env hardcode) regardless of
  what model was assigned to the orchestrator role. Now accepts model_name param
  and falls back to settings value only when registry has no model_name.

- Update ARCH__FUTURE.md: date, running host, local orchestrator status,
  model registry V2 progress, added Cortex Mesh concept (section 9)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/routers/orchestrator.py

@@ -183,6 +183,7 @@ async def _run_job(job_id: str, req: OrchestrateRequest, user: str) -> None:
                 session_messages=session_messages,
                 respond_with_claude=req.respond_with_claude,
                 gemini_api_key=gemini_key,
+                model_name=orch_model.get("model_name") if orch_model else None,
             )
 
         # Save the turn to the session store so it survives a page refresh