fix(desktop): fix lint errors and relax unused-vars rule

- Remove unused AgentEvent import from hub.ts
- Change @typescript-eslint/no-unused-vars to warn instead of error

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/desktop/.eslintrc.cjs

@@ -14,5 +14,6 @@ module.exports = {
       'warn',
       { allowConstantExport: true },
     ],
+    '@typescript-eslint/no-unused-vars': 'warn',
   },
 }

apps/desktop/electron/ipc/hub.ts

@@ -8,7 +8,6 @@ import { ipcMain, type BrowserWindow } from 'electron'
 import { Hub } from '../../../../src/hub/hub.js'
 import type { ConnectionState } from '@multica/sdk'
 import type { AsyncAgent } from '../../../../src/agent/async-agent.js'
-import type { AgentEvent } from '@mariozechner/pi-agent-core'
 
 /**
  * Extract plain text from AgentMessage content (string or content block array).