Adds components/MarkdownDiff.tsx, a theme-bridging shim over
@plannotator/markdown-editor's frozen two-revision diff, mirroring the
MarkdownEditor shim exactly: ThemeProvider mode bridge, plannotator.css
theme import, extensions passthrough (wikiLinks composes), gridEnabled ->
the same design-system card chrome. Hosts import it from
@plannotator/ui/components/MarkdownDiff; AtomicDiffEditor and
@plannotator/atomic-editor stay off the allowlist.
Deps: @plannotator/markdown-editor ^0.4.0, @plannotator/atomic-editor
^0.8.0 (single lockfile copy each), plus @codemirror/merge — the engine's
new required peer — declared directly per the CM6 single-copy discipline.
Tests pin the seam end-to-end: public export surface + types, byte-exact
getMarkdown()/getOriginalMarkdown() incl. CRLF/trailing-space fixtures,
contenteditable="false" frozen contract, change navigation, wiki-link
composition through the shim, and theme/host-class forwarding. The
strict-consumer tsconfig now typechecks the new module.
Michael Ramos