feat: preview workspace component

[starkiVector-090]

Here's what was done:

Root causes:

1. vitest.config.ts was missing @craft/types and @craft/stellar source aliases — the
   test runner couldn't resolve these workspace packages since they have no built dist/
2. PreviewWorkspace.test.tsx used jest.mock (Jest API) instead of vi.mock (Vitest API)
3. PreviewWorkspace.test.ts contained JSX in a .ts file (esbuild rejects this) and was
   a duplicate of the .tsx test

Changes made:

• vitest.config.ts — added @craft/types and @craft/stellar aliases pointing to their
  source directories
• PreviewWorkspace.test.tsx — replaced jest.mock with vi.mock, added
  vi/describe/it/expect/beforeEach imports from vitest
• Deleted PreviewWorkspace.test.ts — it was a duplicate with broken JSX-in-.ts syntax

The preview workspace components themselves (PreviewWorkspace, PreviewControls,
PreviewIframe) were already correctly implemented and needed no changes.
closes #21