feat: add Vue SFC language support (tree-sitter + Volar LSP)

[jafreck]

Summary

Add Vue Single File Component (SFC) support via tree-sitter + Volar LSP, leveraging existing TypeScript infrastructure.

Tooling

Component	Tool	Notes
Tree-sitter grammar	tree-sitter-vue	Stable, widely used
LSP server	vue-language-server (Volar)	Official Vue team, very active, TypeScript-grade intelligence
SCIP indexer	None	N/A

What to implement

Phase 1: Script block extraction

• Add tree-sitter-vue as an npm dependency
• Create src/indexer/extractors/vue.ts:
  • Parse the SFC structure to locate <script> and <script setup> blocks
  • Delegate <script> content to the existing TypeScript/JavaScript extractor for symbol and call-ref extraction
  • Extract component name from defineComponent({ name: '...' }) or <script setup> filename convention
  • Extract defineProps(), defineEmits(), defineExpose() as interface-like symbols
  • Extract import statements from <script> as file imports
• Register vue in SourceIndexStage EXTRACTORS map and ParserPool LANG_PACKAGES
• Add vue-language-server to src/indexer/lsp/registry.ts: { command: 'vue-language-server', args: ['--stdio'] }
• Add file extension .vue to walker
• Add test fixtures in tests/fixtures/vue/
• Add extractor tests

Phase 2: Template component references (follow-up)

• Extract <ComponentName /> usage in <template> as call refs (component invocation edges)
• Resolve component names to their import sources
• Extract v-slot, v-bind, v-on directive targets as refs

Language notes

• Vue SFCs have three sections: <template>, <script>, <style> — only <script> is relevant for the call graph
• <script setup> (Vue 3 Composition API) is syntactic sugar where top-level bindings are automatically exposed
• Volar provides full TypeScript-level type checking inside templates, making LSP enrichment very effective
• Component-to-component edges (<MyChild />) are the primary structural relationship in Vue apps
• Vue 3 composables (useXxx() functions) are the main call-graph pattern in modern Vue code

Context

Vue is a top-3 web framework. Most Vue projects are TypeScript-based, so the existing TS extractor handles the script logic. The main value-add is recognizing the SFC structure and component references.