feat: peek into <style> blocks in HTML/Vue files (#151)

[pranaygp]

Summary

Closes #151

Adds same-file CSS support: when peeking from a class="...", id="...", or HTML tag in an HTML or Vue document, the extension now also resolves selectors defined in any <style> block within the same file.

• New server/src/core/embeddedStyles.ts uses vscode-html-languageservice's scanner (already a dep) to locate <style> regions and reads any lang="scss|sass|less" attribute to pick the right CSS parser.
• The embedded virtual TextDocument reuses the host document's URI and masks everything outside the <style> region with whitespace (preserving newlines), so symbol positions line up exactly with the host file — peek/goto jumps to the correct line without any coordinate translation.
• findSymbols/findDefinition accept an optional in-memory embeddedStylesheetMap that's merged with the persistent StylesheetMap. The persistent cache wins on key collision; embedded entries use fragment-suffixed keys so collisions don't happen in practice.
• Only runs for html and vue documents — JS/TS/etc. peek paths are unchanged.

Test plan

• yarn build passes with zero TS errors
• yarn lint passes
• yarn test — 27 tests pass, including three new cases:
  • class defined in <style> block is found in the same HTML file
  • id defined in <style> block is found in the same HTML file
  • non-HTML/Vue documents yield no embedded stylesheets
• Fixture tests/fixture/example.html updated with a <style> block containing .embedded-class and #embedded-id plus matching usages in the body

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds support for resolving CSS selectors defined in embedded <style> blocks within the same HTML/Vue document, enabling Peek/Go to Definition to jump directly to in-file styles (addressing #151 / “Same File CSS”).

Changes:

• Added embedded <style> block extraction for html/vue documents using vscode-html-languageservice scanning and creation of masked “virtual” CSS documents aligned to host offsets.
• Extended findSymbols / findDefinition to accept an optional in-memory embedded stylesheet map merged with the existing persistent stylesheet cache.
• Added/updated tests and fixtures to validate same-file class/id resolution and to ensure non-HTML/Vue documents don’t produce embedded stylesheets.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
server/src/core/embeddedStyles.ts	New helper to scan HTML/Vue docs for <style> blocks and produce aligned virtual TextDocuments for symbol extraction.
server/src/core/findDefinition.ts	Adds optional embedded stylesheet map support and merges it with the persistent stylesheet cache for symbol/definition lookup.
server/src/server.ts	Integrates embedded <style> lookup into the LSP onDefinition path for HTML/Vue documents.
tests/src/findDefinition.test.ts	Adds coverage for same-file embedded <style> class/id definitions and non-html/vue behavior.
tests/fixture/example.html	Extends fixture with an embedded <style> block and matching usages.

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