refactor: improve TypeScript patterns in test files (Group 1/8) (#8253)

## Summary
Improves type safety in test files by replacing unsafe type patterns
with proper TypeScript idioms.

## Changes
- Define typed `TestWindow` interface extending `Window` for Playwright
tests with custom properties
- Use `Partial<HTMLElement>` with single type assertion for DOM element
mocks
- Remove redundant type imports
- Fix `console.log` → `console.warn` in test fixture

## Files Changed
16 test files across browser_tests, packages, and src/components

## Test Plan
- ✅ `pnpm typecheck` passes
- ✅ No new `any` types introduced
- ✅ All pre-commit hooks pass

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8253-refactor-improve-TypeScript-patterns-in-test-files-Group-1-8-2f16d73d365081548f9ece7bcf0525ee)
by [Unito](https://www.unito.io)

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

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()