fix(extension): clear currentTabId in storage on TabsController.init

Reset currentTabId via updateCurrentTabId(null) so the storage projection
stays consistent with isAgentRunning. Prevents the previous run's tab from
briefly flashing the mask when a new run starts within the heartbeat window.

Closes #550

packages/extension/src/agent/TabsController.ts

@@ -42,7 +42,7 @@ export class TabsController {
 			throw new Error('TabsController already disposed')
 		}
 
-		this.currentTabId = null
+		await this.updateCurrentTabId(null)
 		this.disposed = false
 		this.port = undefined
 		this.portRetries = 0