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>

browser_tests/fixtures/utils/litegraphUtils.ts

@@ -119,8 +119,7 @@ class NodeSlotReference {
           window['app'].canvas.ds.convertOffsetToCanvas(rawPos)
 
         // Debug logging - convert Float64Arrays to regular arrays for visibility
-        // eslint-disable-next-line no-console
-        console.log(
+        console.warn(
           `NodeSlotReference debug for ${type} slot ${index} on node ${id}:`,
           {
             nodePos: [node.pos[0], node.pos[1]],