refactor(8.0): rename HNSWIndex class → JsHnswVectorIndex (scaffold step 3)

Step 3 of the brainy 8.0 rename scaffolding. The class name now matches
its role: the JS HNSW implementation of the VectorIndexProvider contract.
Per planning § 2.3: this is NOT cosmetic — leaving HNSWIndex when the
public contract is VectorIndexProvider creates a confusing read at the
implementation layer.

CHANGES

Repo-wide mechanical rename: HNSWIndex → JsHnswVectorIndex across 52
references in src/ + 5 references in tests/ via sed. Class declaration,
imports, JSDoc, comments, and identifiers all updated.

src/index.ts
- Primary public export: JsHnswVectorIndex (the new name).
- Backwards-compat alias: `export const HNSWIndex = JsHnswVectorIndex`
  with @deprecated note. Removed in the final 8.0 cleanup commit.

NO-OP scope

No behavioural change. The class is exactly the same; only the name
moved. Tests + build green.

VERIFICATION

- npx tsc --noEmit: clean
- npm test: 1468 / 1468 unit

src/hnsw/hnswIndex.ts

@@ -31,10 +31,10 @@ const DEFAULT_CONFIG: HNSWConfig = {
 
 /**
  * Implements {@link VectorIndexProvider}: the vector-index surface Brainy calls
- * on whatever the `'vector'` factory returns (its own `HNSWIndex`, or a native
+ * on whatever the `'vector'` factory returns (its own `JsHnswVectorIndex`, or a native
  * acceleration provider).
  */
-export class HNSWIndex implements VectorIndexProvider {
+export class JsHnswVectorIndex implements VectorIndexProvider {
   private nouns: Map<string, HNSWNoun> = new Map()
   private entryPointId: string | null = null
   private maxLevel = 0
@@ -71,7 +71,7 @@ export class HNSWIndex implements VectorIndexProvider {
   // COW (Copy-on-Write) support
   private cowEnabled: boolean = false
   private cowModifiedNodes: Set<string> = new Set()
-  private cowParent: HNSWIndex | null = null
+  private cowParent: JsHnswVectorIndex | null = null
 
   // Deferred HNSW persistence for cloud storage performance
   // In deferred mode, HNSW connections are only persisted on flush/close
@@ -130,7 +130,7 @@ export class HNSWIndex implements VectorIndexProvider {
    * Lifecycle: brainy.ts wires this after plugin activation when (a) the
    * `vectorStore:mmap` provider is registered AND (b) the storage adapter
    * resolves a real local path via `getBinaryBlobPath()`. Cloud adapters
-   * leave it null; HNSWIndex's behaviour is then identical to pre-2.4.0.
+   * leave it null; JsHnswVectorIndex's behaviour is then identical to pre-2.4.0.
    */
   public setVectorBackend(backend: MmapVectorBackend | null): void {
     this.vectorBackend = backend
@@ -340,10 +340,10 @@ export class HNSWIndex implements VectorIndexProvider {
    *
    * @example
    * ```typescript
-   * const parent = new HNSWIndex(config)
+   * const parent = new JsHnswVectorIndex(config)
    * // ... parent has 1M nodes ...
    *
-   * const fork = new HNSWIndex(config)
+   * const fork = new JsHnswVectorIndex(config)
    * fork.enableCOW(parent) // <10ms - instant!
    *
    * // Reads share data
@@ -353,7 +353,7 @@ export class HNSWIndex implements VectorIndexProvider {
    * await fork.addItem(newItem) // Deep copies only modified nodes
    * ```
    */
-  public enableCOW(parent: HNSWIndex): void {
+  public enableCOW(parent: JsHnswVectorIndex): void {
     this.cowEnabled = true
     this.cowParent = parent