feat: Enforce exclusive auto-request (one client at a time)

Server is now source of truth for autoRequest. When a client enables it,
all other clients lose it. Broadcast includes autoRequest per client,
frontend syncs from server state on each torch-update.

frontend/src/components/TorchButton.vue

@@ -2,7 +2,7 @@
 import { ref, computed, onMounted, onUnmounted, nextTick } from 'vue'
 import { useTorchStore } from '../stores/torch'
 import { useCanvasStore } from '../stores/canvas'
-import { requestTorch, releaseTorch, transferTorch, updateName } from '../services/torch'
+import { requestTorch, releaseTorch, transferTorch, updateName, setAutoRequest } from '../services/torch'
 
 const torchStore = useTorchStore()
 const canvasStore = useCanvasStore()
@@ -86,7 +86,7 @@ async function handleTransfer(targetId: string) {
 }
 
 function toggleAutoRequest() {
-  torchStore.setAutoRequest(!torchStore.autoRequest)
+  setAutoRequest(!torchStore.autoRequest)
 }
 
 onMounted(() => {

frontend/src/services/torch.ts

@@ -94,6 +94,12 @@ async function handleMessage(data: any) {
         await connectToMCP()
       }
 
+      // Sync autoRequest from server (server is source of truth)
+      const myClient = data.clients.find((c: any) => c.id === clientId)
+      if (myClient && myClient.autoRequest !== torchStore.autoRequest) {
+        torchStore.setAutoRequest(myClient.autoRequest)
+      }
+
       // Auto-request: if no one holds the torch and we have autoRequest enabled
       if (!hasTorchNow && data.holderId === null && torchStore.autoRequest) {
         console.log('[Torch] Auto-requesting torch (no holder)')
@@ -163,6 +169,15 @@ export async function transferTorch(targetId: string): Promise<boolean> {
   return true
 }
 
+/**
+ * Toggle auto-request on server (exclusive — only one client at a time)
+ */
+export function setAutoRequest(value: boolean): void {
+  if (torchWs?.readyState === WebSocket.OPEN) {
+    torchWs.send(JSON.stringify({ type: 'set-auto-request', value }))
+  }
+}
+
 /**
  * Update client name on server
  */

frontend/src/stores/torch.ts

@@ -4,6 +4,7 @@ import { ref, computed } from 'vue'
 export interface TorchClient {
   id: string
   name: string
+  autoRequest: boolean
   userAgent: string
   hostname: string
   url: string