Test modernization: add Vitest unit lane and begin suite migration split

[johnpapa]

Summary

Let's speed up and modernize the tests!

Execute the approved test modernization plan for johnpapa/vscode-peacock using a phased approach:

• Total tests: 257
  • 200 extension/live-share tests
  • 57 docs e2e Playwright tests
• Current skipped tests: 1 (src/test/suite/status-bar.test.ts uses suite.skip)
• Target split for extension/live-share tests:
  • 130 unit-fast tests (Vitest lane)
  • 70 host contract tests (VS Code host lane)
  • 57 docs e2e tests unchanged
• Refactor scope: 14 suite files / 140 tests require extraction-and-split

Approved per-file migration table

#	File	Tests	Planned lane split	Refactor level
1	src/test/suite/affected-elements.test.ts	40	Split Unit 36 / Host 4	High refactor
2	src/test/suite/activity-bar-top.test.ts	9	Split Unit 7 / Host 2	Medium
3	src/test/suite/basic.test.ts	7	Host 7	No refactor
4	src/test/suite/built-in-colors.test.ts	8	Split Unit 5 / Host 3	Medium
5	src/test/suite/color-input.test.ts	26	Split Unit 24 / Host 2	High
6	src/test/suite/config-changes.test.ts	5	Host 5	No refactor
7	src/test/suite/current-color.test.ts	4	Host 4	No refactor
8	src/test/suite/cursor-titlebar.test.ts	2	Split Unit 1 / Host 1	Low
9	src/test/suite/darken-lighten.test.ts	2	Split Unit 1 / Host 1	Low
10	src/test/suite/documentation.test.ts	1	Host 1	No refactor
11	src/test/suite/editing-color-settings.test.ts	24	Split Unit 20 / Host 4	High
12	src/test/suite/element-adjustments.test.ts	7	Split Unit 5 / Host 2	Medium
13	src/test/suite/excluded-settings.test.ts	3	Split Unit 2 / Host 1	Medium
14	src/test/suite/favorite-colors.test.ts	4	Split Unit 3 / Host 1	Medium
15	src/test/suite/foreground.test.ts	6	Unit 6	Low
16	src/test/suite/notification.test.ts	2	Unit 2	No refactor
17	src/test/suite/object-library.test.ts	12	Unit 12	No refactor
18	src/test/suite/remote.test.ts	13	Host 13	No refactor
19	src/test/suite/reset.test.ts	4	Host 4	No refactor
20	src/test/suite/save-favorite-color.test.ts	3	Split Unit 2 / Host 1	Medium
21	src/test/suite/save-starter-favorite-colors.test.ts	3	Split Unit 2 / Host 1	Medium
22	src/test/suite/set-sidebar-darkness-level.test.ts	3	Split Unit 2 / Host 1	Medium
23	src/test/suite/status-bar.test.ts	1	Host 1 skipped	Optional rehab/removal decision
24	src/test/suite/surprise-me-on-startup.test.ts	3	Host 3	No refactor
25	src/live-share/test/suite/live-share.test.ts	8	Host 8	No refactor
26	e2e/homepage.spec.ts	7	E2E unchanged	—
27	e2e/images.spec.ts	4	E2E unchanged	—
28	e2e/links.spec.ts	5	E2E unchanged	—
29	e2e/navigation.spec.ts	8	E2E unchanged	—
30	e2e/pages.spec.ts	9	E2E unchanged	—
31	e2e/screenshots.spec.ts	9	E2E unchanged	—
32	e2e/search.spec.ts	5	E2E unchanged	—
33	e2e/styling.spec.ts	10	E2E unchanged	—

First implementation slice

1. Add Vitest setup and scripts (test:unit, test:host) while preserving current host runner.
2. Move pure suites first (object-library, notification) to the unit lane.
3. Begin split pattern with low-risk files (foreground and one split suite such as cursor-titlebar) to prove extraction + host/unit separation.
4. Keep changes focused and reviewable with docs/changelog updates and CI-ready checks.