refactor: wrap tunnel connect/disconnect operations in spawn_blocking and add pending state UI feedback

Move tunnel_manager::connect and disconnect calls into spawn_blocking tasks to prevent blocking async runtime. Clone app handle and profile path before spawning. Add map_err for task join failures.

Add tunnelActionPending state to track in-progress tunnel operations. Pass busy prop to AppHeader and disable sync/logout/connect buttons during tunnel actions. Update connect button text to show "

desktop-client/src/components/AppHeader.tsx

@@ -1,6 +1,7 @@
 import { ActionButton } from "./ActionButton";
 
 type AppHeaderProps = {
+  busy: boolean;
   enrolled: boolean;
   connected: boolean;
   syncing: boolean;
@@ -10,6 +11,7 @@ type AppHeaderProps = {
 };
 
 export function AppHeader({
+  busy,
   enrolled,
   connected,
   syncing,
@@ -36,10 +38,10 @@ export function AppHeader({
         <div className="header-actions-secondary">
           {enrolled ? (
             <>
-              <ActionButton disabled={syncing} onClick={onSync} variant="secondary">
+              <ActionButton disabled={busy || syncing} onClick={onSync} variant="secondary">
                 {syncing ? "Syncing..." : "Sync"}
               </ActionButton>
-              <ActionButton onClick={onLogout} variant="ghost">
+              <ActionButton disabled={busy || syncing} onClick={onLogout} variant="ghost">
                 Logout
               </ActionButton>
             </>
@@ -47,11 +49,11 @@ export function AppHeader({
         </div>
         <div className="header-actions-primary">
           <ActionButton
-            disabled={!enrolled}
+            disabled={!enrolled || busy || syncing}
             onClick={onToggleConnection}
             variant={connected ? "danger" : "primary"}
           >
-            {!enrolled ? "Provision first" : connected ? "Disconnect" : "Connect"}
+            {!enrolled ? "Provision first" : busy ? connected ? "Disconnecting..." : "Connecting..." : connected ? "Disconnect" : "Connect"}
           </ActionButton>
         </div>
       </div>