fix: clarify one-token-per-host requirement and improve stale agent cleanup

- Setup wizard now clearly states 'Use a different token for each host'
- New Token button is always visible and more prominent (blue styling)
- WebSocket store now clears stale agents (>60s since lastSeen) immediately
  when receiving empty host arrays, instead of waiting for 3 consecutive updates

frontend-modern/src/components/SetupWizard/steps/CompleteStep.tsx

@@ -334,12 +334,11 @@ Keep these credentials secure!
                         </svg>
                         Install Command
                     </h3>
-                    <Show when={connectedAgents().length > 0}>
                     <button
                         onClick={generateNewToken}
                         disabled={generatingToken()}
-                            class="text-xs text-white/50 hover:text-white/70 flex items-center gap-1 disabled:opacity-50"
+                        class="text-xs bg-blue-500/20 text-blue-300 hover:bg-blue-500/30 hover:text-blue-200 px-2 py-1 rounded flex items-center gap-1 disabled:opacity-50"
-                            title="Generate a different token if needed for security isolation"
+                        title="Generate a new token for the next host"
                     >
                         {generatingToken() ? (
                             <svg class="w-3 h-3 animate-spin" fill="none" viewBox="0 0 24 24">
@@ -348,15 +347,14 @@ Keep these credentials secure!
                             </svg>
                         ) : (
                             <svg class="w-3 h-3" fill="none" viewBox="0 0 24 24" stroke="currentColor">
-                                    <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M4 4v5h.582m15.356 2A8.001 8.001 0 004.582 9m0 0H9m11 11v-5h-.581m0 0a8.003 8.003 0 01-15.357-2m15.357 2H15" />
+                                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 4v16m8-8H4" />
                             </svg>
                         )}
-                            Different Token
+                        New Token
                     </button>
-                    </Show>
                 </div>
                 <p class="text-white/70 text-xs mb-2">
-                    Run this command on any host you want to monitor. Use the same command on multiple servers.
+                    Run on the host you want to monitor. <span class="text-amber-300">Use a different token for each host</span> - click "New Token" after each install.
                 </p>
 
                 <div class="bg-black/40 rounded-lg p-2.5 font-mono text-[10px] mb-2 relative group">