fix(rpc): detect mid-session disconnects and stop blocking the UI thread

The connection state machine never tore down on a lost connection: refresh-loop
RPC errors were swallowed, rpc_->isConnected() stayed true after a daemon
crash/restart/socket drop, and the UI showed stale balances with no reconnect.
Several operations also ran synchronous curl straight from ImGui handlers.

- Add handleLostConnection(): after N consecutive cycles where BOTH core RPCs
  fail (warmup excluded, so no reconnect loop), disconnect so update()'s
  reconnect branch re-enters tryConnect().
- Move banPeer/unbanPeer/clearBans and key export/import onto the worker thread
  (import requests a rescan that could freeze the UI for the curl timeout).
- Run the block-info dialog's two chained RPCs on the worker thread (+ guard the
  getblockhash result type).
- Detect daemon warmup via the JSON-RPC -28 code (new RpcError carrying the code;
  message text preserved so 401/warmup string-matching is unaffected), and widen
  CONNECTTIMEOUT to 10s for remote/TLS hosts (2s localhost).

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

src/ui/windows/block_info_dialog.cpp

@@ -5,6 +5,7 @@
 #include "block_info_dialog.h"
 #include "../../app.h"
 #include "../../rpc/rpc_client.h"
+#include "../../rpc/rpc_worker.h"
 #include "../../util/i18n.h"
 #include "../notifications.h"
 #include "../schema/ui_schema.h"
@@ -124,14 +125,31 @@ void BlockInfoDialog::render(App* app)
         }
         
         if (material::StyledButton(TR("block_get_info"), ImVec2(0,0), S.resolveFont(closeBtn.font))) {
-            if (rpc && rpc->isConnected()) {
+            if (rpc && rpc->isConnected() && app->worker()) {
                 s_loading = true;
                 s_error.clear();
                 s_has_data = false;
                 s_pending_app = app;
-                
-                // Use getBlock(height) which uses UnifiedCallback
-                rpc->getBlock(s_height, handleBlockResponseUnified);
+
+                // Run the two chained RPCs (getblockhash → getblock) on the worker thread;
+                // doing them inline froze the UI for two round-trips. Guard the hash type.
+                int height = s_height;
+                app->worker()->post([rpc, height]() -> rpc::RPCWorker::MainCb {
+                    json block;
+                    std::string error;
+                    try {
+                        rpc::RPCClient::TraceScope trace("Explorer / Block info");
+                        auto hashResult = rpc->call("getblockhash", {height});
+                        if (!hashResult.is_string()) {
+                            error = "unexpected getblockhash result";
+                        } else {
+                            block = rpc->call("getblock", {hashResult.get<std::string>()});
+                        }
+                    } catch (const std::exception& e) {
+                        error = e.what();
+                    }
+                    return [block, error]() { handleBlockResponseUnified(block, error); };
+                });
             }
         }