fix: Lazy grammar loading and quantized embeddings to prevent V8 WASM OOM

Fixes #54 — `codegraph init -i` crashes with "Fatal process out of memory: Zone"
on large codebases because all 16 tree-sitter WASM grammar modules were compiled
upfront by V8, exhausting the WASM Zone allocator.

Changes:
- initGrammars() now only initializes the tree-sitter WASM runtime (Parser.init()),
  no longer eagerly loads all grammar files
- New loadGrammarsForLanguages() loads only grammars for languages actually present
  in the project (e.g. a Dart project loads ~2-3 grammars instead of 16)
- Orchestrator detects needed languages after file scan, before parsing begins
- Embedding pipeline now uses quantized model (~67MB vs ~270MB) to further reduce
  WASM memory pressure when embeddings are enabled

src/index.ts

@@ -61,7 +61,7 @@ export {
   CODEGRAPH_DIR,
 } from './directory';
 export { IndexProgress, IndexResult, SyncResult } from './extraction';
-export { detectLanguage, isLanguageSupported, getSupportedLanguages, initGrammars } from './extraction';
+export { detectLanguage, isLanguageSupported, isGrammarLoaded, getSupportedLanguages, initGrammars, loadGrammarsForLanguages, loadAllGrammars } from './extraction';
 export { ResolutionResult } from './resolution';
 export { EmbeddingProgress } from './vectors';
 export {