feat: add SQ8 vector quantization, lazy loading, and two-phase rerank to HNSW

- SQ8 scalar quantization (8-bit) for 4x vector storage reduction
- Lazy vector loading: evict float32 vectors after graph construction,
  load on-demand from storage via UnifiedCache
- Two-phase search: over-retrieve with SQ8 approximate distances,
  rerank top candidates with exact float32 distances
- Configuration surface: hnsw.quantization and hnsw.vectorStorage in BrainyConfig
- All features disabled by default (zero behavior change for existing users)
- 27 new tests covering quantization accuracy, lazy loading, reranking
- Remove GitHub Actions CI (build locally, cortex CI handles native builds)

src/brainy.ts

@@ -6236,7 +6236,14 @@ export class Brainy<T = any> implements BrainyInterface<T> {
   private setupIndex(): HNSWIndex | TypeAwareHNSWIndex {
     const indexConfig = {
       ...this.config.index,
-      distanceFunction: this.distance
+      distanceFunction: this.distance,
+      // Wire HNSW optimization config (v7.11.0)
+      quantization: this.config.hnsw?.quantization ? {
+        enabled: this.config.hnsw.quantization.enabled ?? false,
+        bits: this.config.hnsw.quantization.bits ?? 8,
+        rerankMultiplier: this.config.hnsw.quantization.rerankMultiplier ?? 3
+      } : undefined,
+      vectorStorage: this.config.hnsw?.vectorStorage
     }
 
     const persistMode = this.resolveHNSWPersistMode()
@@ -6368,6 +6375,8 @@ export class Brainy<T = any> implements BrainyInterface<T> {
       reservedQueryMemory: config?.reservedQueryMemory ?? undefined as any,
       // HNSW persistence mode - undefined = smart default in setupIndex
       hnswPersistMode: config?.hnswPersistMode ?? undefined as any,
+      // HNSW optimization options (v7.11.0)
+      hnsw: config?.hnsw ?? undefined as any,
       // Embedding initialization - false = lazy init on first embed()
       eagerEmbeddings: config?.eagerEmbeddings ?? false,
       // Integration Hub - undefined/false = disabled