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/transaction/operations/IndexOperations.ts

@@ -2,14 +2,14 @@
  * Index Operations with Rollback Support
  *
  * Provides transactional operations for all indexes:
- * - HNSWIndex (unified vector index)
+ * - JsHnswVectorIndex (unified vector index)
  * - MetadataIndexManager (roaring bitmap filtering)
  * - GraphAdjacencyIndex (LSM-tree graph storage)
  *
  * Each operation can be executed and rolled back atomically.
  */
 
-import type { HNSWIndex } from '../../hnsw/hnswIndex.js'
+import type { JsHnswVectorIndex } from '../../hnsw/hnswIndex.js'
 import type { MetadataIndexManager } from '../../utils/metadataIndex.js'
 import type { GraphAdjacencyIndex } from '../../graph/graphAdjacencyIndex.js'
 import type { GraphVerb } from '../../coreTypes.js'
@@ -21,13 +21,13 @@ import type { Operation, RollbackAction } from '../types.js'
  * Rollback strategy:
  * - Remove item from index
  *
- * Note: Works with both HNSWIndex and TypeAwareHNSWIndex
+ * Note: Works with both JsHnswVectorIndex and TypeAwareHNSWIndex
  */
 export class AddToHNSWOperation implements Operation {
   readonly name = 'AddToHNSW'
 
   constructor(
-    private readonly index: HNSWIndex,
+    private readonly index: JsHnswVectorIndex,
     private readonly id: string,
     private readonly vector: number[]
   ) {}
@@ -76,7 +76,7 @@ export class RemoveFromHNSWOperation implements Operation {
   readonly name = 'RemoveFromHNSW'
 
   constructor(
-    private readonly index: HNSWIndex,
+    private readonly index: JsHnswVectorIndex,
     private readonly id: string,
     private readonly vector: number[] // Required for rollback
   ) {}
@@ -211,7 +211,7 @@ export class BatchAddToHNSWOperation implements Operation {
   private operations: AddToHNSWOperation[]
 
   constructor(
-    index: HNSWIndex,
+    index: JsHnswVectorIndex,
     items: Array<{ id: string; vector: number[] }>
   ) {
     this.operations = items.map(