…o @mdview/core

…Adapter

Move dom-purifier, skeleton-renderer, and scroll-manager to
packages/core/src/utils/ and replace originals with re-export shims.
Update render-pipeline and its test to use local imports. Add dompurify
dependency to @mdview/core package.json.

Move worker-pool, render-worker, and task modules (parse, highlight,
mermaid) to packages/core/src/workers/. Original files replaced with
re-export shims. Worker-pool uses createDebug() for platform-agnostic
logging instead of importing the Chrome-specific debug singleton.

…derer, and comment UI

…structors

native-host.test.ts: provide explicit mock factories for 'fs' and 'os'
since vitest auto-mocking doesn't work with Node built-ins.

comment-manager.test.ts: convert vi.fn() constructor mocks from arrow
functions to function(this) syntax since arrow functions can't be used
as constructors with `new`.