feat: add neural extraction APIs with NounType taxonomy

Add brain.extract() and brain.extractConcepts() methods that use
NeuralEntityExtractor with embeddings and sophisticated NounType
taxonomy (30+ entity types) for semantic entity and concept extraction.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/vfs/semantic/index.ts

@@ -0,0 +1,28 @@
+/**
+ * Semantic VFS - Index
+ *
+ * Central export point for all semantic VFS components
+ */
+
+// Core components
+export { SemanticPathParser } from './SemanticPathParser.js'
+export type {
+  SemanticDimension,
+  ParsedSemanticPath,
+  RelationshipValue,
+  SimilarityValue
+} from './SemanticPathParser.js'
+
+export { ProjectionRegistry } from './ProjectionRegistry.js'
+export type { ProjectionStrategy } from './ProjectionStrategy.js'
+export { BaseProjectionStrategy } from './ProjectionStrategy.js'
+
+export { SemanticPathResolver } from './SemanticPathResolver.js'
+
+// Built-in projections
+export { ConceptProjection } from './projections/ConceptProjection.js'
+export { AuthorProjection } from './projections/AuthorProjection.js'
+export { TemporalProjection } from './projections/TemporalProjection.js'
+export { RelationshipProjection } from './projections/RelationshipProjection.js'
+export { SimilarityProjection } from './projections/SimilarityProjection.js'
+export { TagProjection } from './projections/TagProjection.js'