chore: add vitest browser mode for component tests

[johnleider]

Summary

• Add Vitest browser mode (Playwright/chromium) for all 30 component tests
• Dual-project vitest config: v0:unit (happy-dom) for composable/utility tests, v0:browser (Playwright) for component tests
• Component test files renamed from *.test.ts to *.browser.test.ts to distinguish test types
• Remove happy-dom workarounds (showPopover/hidePopover mocks) from Select, Combobox, and Dialog — real browser has native APIs
• Test infrastructure in packages/0/test/ with browser commands (drag, waitStable, focus/motion emulation), setup, and shared utilities

Changes

Area	What
Dependencies	@vitest/browser-playwright, @testing-library/vue, jsdom added to catalog
Config	vitest.config.ts → unit project, new vitest.browser.config.ts → browser project
Root config	Updated to reference both package configs
Test infra	packages/0/test/ — commands.ts, setup.ts, globals.d.ts, index.ts
Renames	30 component tests: index.test.ts → index.browser.test.ts
Cleanup	Removed showPopover/hidePopover/showModal mocks, removed happy-dom comments
Scripts	Added test:unit, test:browser, test:open to packages/0

Test plan

• pnpm vitest run --project v0:unit — 75 files, 2976 tests passing
• pnpm vitest run --project v0:browser — 30 component test files (requires Playwright chromium; cannot verify in WSL)
• pnpm typecheck — clean
• pnpm lint:fix — clean

[pkg-pr-new]

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commit: 4d91efe