Fix shutdown race conditions causing bad_weak_ptr crash (v5.4.1)

Fixes multiple concurrency bugs exposed during shutdown when Tor proxy
connections are failing:

- Reorder shutdown: stop network threads before destroying Tor V3 services
- Make RPC listener responsive to fShutdown (poll_one+sleep vs blocking run_one)
- Wrap StopRequests() in try/catch and drain io_service on exit
- Fix leaked CNode AddRef in ThreadSocketHandler2 and ThreadMessageHandler2
  (return→break so Release loop executes)
- Guard vNodes.size() read with cs_vNodes lock (data race)
- Guard Qt UI signal callbacks with fShutdown check (use-after-free)
- Add cs_vNodes lock in CNetCleanup global destructor
- Force-disconnect remaining nodes in StopNode() after threads stop
- Make Tor maintenance thread sleep in 500ms intervals for prompt shutdown

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

src/tor/onion_v3.cpp

@@ -2206,7 +2206,9 @@ void ThreadTorMaintenance(void* parg)
 
     while (!fShutdown)
     {
-        MilliSleep(30000); // check every 30 seconds
+        // Sleep in short intervals so the thread exits promptly on shutdown
+        for (int i = 0; i < 60 && !fShutdown; i++)
+            MilliSleep(500);
         if (fShutdown) break;
 
         // --- Tor health check & auto-restart ---
@@ -2243,7 +2245,8 @@ void ThreadTorMaintenance(void* parg)
             else
             {
                 printf("WARNING: Tor restart failed, retrying in %d seconds\n", restartBackoffSec);
-                MilliSleep(restartBackoffSec * 1000);
+                for (int i = 0; i < restartBackoffSec * 2 && !fShutdown; i++)
+                    MilliSleep(500);
                 if (restartBackoffSec < 300)
                     restartBackoffSec *= 2;
             }