Port upstream reference linked image click fix

[Renakoni]

Upstream

Ports marktext/marktext#4866: marktext/marktext#4866

This is stacked on #73 (sync/upstream-4858-linked-image-modifier-click) because upstream #4866 depends on #4858's exported LINK_SELECTOR, linked-image modifier-click guard, and linked-image regression test.

Android relevance

Android carries the same Muya inline tokenizer, image renderer, CSS, and image/link click handlers. Reference-linked README badges ([![alt](img)][ref]) and raw-HTML linked images can appear in Markdown edited on Android, so the same rendering and event behavior applies in the WebView editor.

Changes

• Allow reference_link tokenization to capture image link text, so [![alt](img)][ref] becomes one reference link wrapping the image instead of a bare image plus fragmented reference link.
• Render inline-image hover controls as span instead of nested a elements, preventing invalid <a> inside <a> markup when an image is inside a real reference/raw-HTML anchor.
• Relax the image icon CSS selectors from a.mu-image-icon-* to .mu-image-icon-* to match the new span controls.
• Extend linked image click coverage for reference-linked images.
• Add tokenizer coverage for image reference-link anchors.
• Add jsdom coverage for raw-HTML linked images, where the real anchor nesting behavior is observable.

Verification

• pnpm --dir third_party/muya exec vitest run src/inlineRenderer/__tests__/referenceLinkImageAnchor.spec.ts src/selection/__tests__/linkedImageClick.spec.ts src/selection/__tests__/rawHtmlLinkedImageClick.spec.ts
• pnpm build