test: remove any type from BaseTerminal test mock access

- Replace `as any` with proper `Mock` type from vitest
- Import Mock type and access mock.calls with type safety
- Explicitly type selectionCallback as `() => void`
- Break down mock access into steps for clarity

Part of Phase 2 - Quick wins (1 instance removed)

src/components/bottomPanel/tabs/terminal/BaseTerminal.test.ts

@@ -1,6 +1,7 @@
 import { createTestingPinia } from '@pinia/testing'
 import type { VueWrapper } from '@vue/test-utils'
 import { mount } from '@vue/test-utils'
+import type { Mock } from 'vitest'
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import { nextTick } from 'vue'
 import { createI18n } from 'vue-i18n'
@@ -151,8 +152,8 @@ describe('BaseTerminal', () => {
     // Trigger the selection change callback that was registered during mount
     expect(mockTerminal.onSelectionChange).toHaveBeenCalled()
     // Access the mock calls - TypeScript can't infer the mock structure dynamically
-    const selectionCallback = (mockTerminal.onSelectionChange as any).mock
-      .calls[0][0]
+    const mockCalls = (mockTerminal.onSelectionChange as Mock).mock.calls
+    const selectionCallback = mockCalls[0][0] as () => void
     selectionCallback()
     await nextTick()