v5.3.7: Fix sync stall, transaction display, balance updates, and bootstrap snapshots

Sync fixes:
- Extend stall detection beyond IBD to catch post-IBD sync gaps
- Walk-forward inv continuation to avoid CBlockLocator exponential gap loop
- Track walk-forward progress for stall recovery without restarting from scratch

GUI fixes:
- Load transactions synchronously in constructor (deferred QTimer never fired)
- Use beginResetModel/endResetModel instead of deprecated reset()
- Schedule full refresh on TRY_LOCK failure to avoid dropped CT_NEW notifications
- Only update cachedNumBlocks after successful balance check (prevents permanent loss)
- Add GetAllBalances() single-pass balance retrieval with TRY_LOCK

Bootstrap:
- Add trusted snapshot manifest verification for bootstrap archives
- Add IsKnownCheckpoint() to validate manifest against compiled-in checkpoints
- Skip txleveldb rebuild when verified manifest is present

Bump version to 5.3.7 across all packaging manifests.

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

src/trianglesrpc.cpp

@@ -787,10 +787,16 @@ static void RPCAcceptHandler(boost::shared_ptr< basic_socket_acceptor<Protocol,
 
     AcceptedConnectionImpl<ip::tcp>* tcp_conn = dynamic_cast< AcceptedConnectionImpl<ip::tcp>* >(conn);
 
-    // TODO: Actually handle errors
     if (error)
     {
+        if (error != asio::error::operation_aborted)
+            printf("RPC accept error from %s: %s (%d)\n",
+                   tcp_conn ? tcp_conn->peer.address().to_string().c_str() : "unknown peer",
+                   error.message().c_str(),
+                   error.value());
         delete conn;
+        vnThreadsRunning[THREAD_RPCLISTENER]--;
+        return;
     }
 
     // Restrict callers by IP.  It is important to