feat(desktop): consume @muyajs/core in util files (markdownToHtml/pdf/dompurify/printService/sourceCode/icon) - #4402

Export the TableChessboard UI plugin from the muya core entrypoint so the
desktop editor host can register it (the quick-insert table picker). The
@muyajs/core workspace dependency and the tsconfig.base.json @muyajs/core
paths entry it consumes already landed on develop via #4402.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

* build(muya): export TableChessboard from @muyajs/core entrypoint

Export the TableChessboard UI plugin from the muya core entrypoint so the
desktop editor host can register it (the quick-insert table picker). The
@muyajs/core workspace dependency and the tsconfig.base.json @muyajs/core
paths entry it consumes already landed on develop via #4402.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

* feat(desktop): exportStyledHTML wrapper + @muyajs/core types shim

@muyajs/core exposes MarkdownToHtml(md, muya).generate() but has no
equivalent of the legacy muyajs exportStyledHTML (which injects a TOC at
the [TOC] marker and wraps the article in a header/footer page table for
PDF/print). Add a desktop-side exportStyledHTML wrapper that reproduces
that behaviour on top of the engine output so export stays equivalent.

Add a hand-written @muyajs/core declaration shim (referenced by the
tsconfig paths entry) so vue-tsc resolves the import at the package
boundary instead of type-checking the entire muya source tree under the
desktop program. Delete it once @muyajs/core ships built type
declarations.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

* feat(desktop): migrate editor.vue to the @muyajs/core engine

Rewire the editor host onto @muyajs/core:

- Construction: build the engine with markRaw(new Muya(el, options)) +
  explicit init(); register the new UI plugin set (TableChessboard,
  ParagraphQuickInsertMenu, CodeBlockLanguageSelector, EmojiSelector,
  ImageEditTool, ImageResizeBar/ToolBar, InlineFormatToolbar,
  ParagraphFront*, PreviewToolBar, LinkTools, FootnoteTool, Table*).
- Options/i18n: map the desktop language preference to the engine's
  bundled locale objects and pass locale on construct + on
  language-changed (editor.locale(...)).
- Events: derive the content-change payload (markdown/wordCount/cursor/
  history/TOC/blocks) from the engine's low-level json-change; adapt the
  new selection-change shape for the application-menu state builder and
  drive format state off the formats it now carries; listen for scroll
  on the container directly (engine has no scroll event).
- Methods: setContent (replacing setMarkdown), getScrollContainer via
  domNode, viewport-relative caret coords for typewriter/keep-visible
  scrolling, copy/paste method remap (copyAsRich -> copyAsHtml), per-tab
  engine-history stash for in-session tab switches with a synthetic
  desktop-shaped history for save/dirty tracking.
- Search circular-ref fix: muya's search/replace/find return the live
  Search instance (circular: Search -> muya -> ... -> ScrollPage) and
  each match carries a live block ref. The store deep-clones (JSON) its
  payload, which crashed; toSearchMatches() strips it to the plain
  { index, matches, value } the search UI needs before dispatching.
- Blur the editor when the command palette opens to avoid a focus-trap
  vs engine-selection deadlock that froze the renderer.

Documented gaps (engine does not yet surface these; editor stays fully
functional): heading-copy-link hover affordance, selection affiliation
chain for block-context menu toggles, and selectedTableCells in
select-all.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

* test(desktop): update e2e selectors + recipes for @muyajs/core mu- DOM

Migrate the desktop e2e suite to the @muyajs/core renderer:

- Swap ag-* DOM selectors for the engine's mu-* equivalents across the
  fixture-render, crash, issue-regression, paragraph-blocks and
  strong-cjk specs, and update helpers.ts (paragraph content lives in
  span.mu-paragraph-content; selection is committed via a synthetic
  keyup so the engine updates its active block).
- crash-update-paragraph #2099: the quick-insert menu now triggers on
  '/' (not the legacy '@'); type '/', wait for the float to be shown
  (it is always attached but parked off-screen until positioned), then
  pick Header 1.
- plantuml: the engine encodes via plantuml-encoder (no '~1' deflate
  prefix), so assert the bare plantuml-alphabet base64 src.
- strong-cjk: mark the CJK + **"x"** flanking case as fixme — a
  documented @muyajs/core parser gap (#4307, tracked as it.fails in
  packages/muya/src/state/__tests__/strongCjkFlanking.spec.ts); the
  CJK + **plain** regression still passes.

Full desktop e2e: 87 passed, 3 skipped (all documented gaps), 0 failed.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

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Co-authored-by: Claude Opus 4.8 (1M context) <[email protected]>