fix(rpc): keep the worker alive on non-std throws; atomic flags

The RPC worker loop only caught std::exception. A task that threw
anything else - a non-std exception propagating out of a posted job -
escaped the loop and tore down the worker thread, so every later RPC
silently went unanswered.

- The worker loop now also has a catch-all that swallows non-std
  throws and keeps the thread running. Such a job still loses its
  main-thread callback, exactly as the std::exception path already
  did; the only change is that the worker survives.
- RPCClient's connected_ and warming_up_ flags are now atomic. They
  are read from the UI thread while the worker updates them, so the
  plain bools were a data race.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/rpc/rpc_worker.cpp

@@ -142,6 +142,10 @@ void RPCWorker::run()
             }
         } catch (const std::exception& e) {
             DEBUG_LOGF("[RPCWorker] Task threw: %s\n", e.what());
+        } catch (...) {
+            // A raw post() job that throws still loses its MainCb (no worse than the
+            // std::exception path); this only keeps the worker thread alive.
+            DEBUG_LOGF("[RPCWorker] Task threw unknown exception\n");
         }
     }
 }