Port upstream linked image modifier click fix

[Renakoni]

Upstream

Ports marktext/marktext#4858: marktext/marktext#4858

This is stacked on #69 (sync/upstream-4861-prism-dependency-order) because the focused Muya tests boot the editor and Android main still has the pre-#4861 Prism dynamic import issue under Vitest.

Android relevance

Android carries the same Muya link and image click handlers. Modifier-click is primarily desktop-style, but Android devices can use hardware keyboards, mice, tablets, and Chromebooks; keeping Muya's event contract aligned also prevents the image preview handler from racing the link handler for linked images.

Changes

• Export Muya's LINK_SELECTOR so image selection can reuse the same definition of link wrappers.
• Suppress image-preview format-click emission when a modifier-clicked image is inside a link wrapper.
• Preserve existing plain-image modifier-click preview behavior.
• Add regression coverage for linked images and plain images.

Verification

• pnpm --dir third_party/muya exec vitest run src/selection/__tests__/linkedImageClick.spec.ts src/selection/__tests__/duplicateImageResize.spec.ts src/selection/__tests__/parityPreviewImage.spec.ts src/__tests__/formatClickEvents.spec.ts
• pnpm build