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/plugin.ts

@@ -62,7 +62,7 @@ export interface BrainyPluginContext {
    * - 'graphIndex'         — GraphAdjacencyIndex replacement
    * - 'entityIdMapper'     — EntityIdMapper replacement
    * - 'cache'              — UnifiedCache replacement
-   * - 'hnsw'               — HNSWIndex replacement
+   * - 'hnsw'               — JsHnswVectorIndex replacement
    * - 'roaring'            — RoaringBitmap32 replacement
    * - 'embeddings'         — Embedding engine replacement (single text)
    * - 'embedBatch'         — Batch embedding engine (texts[] → vectors[])
@@ -88,7 +88,7 @@ export interface BrainyPluginContext {
 // (Cortex) that declares `implements MetadataIndexProvider` gets a compile
 // error the moment a method Brainy depends on is dropped or its signature
 // drifts. Brainy's own baseline classes (`MetadataIndexManager`,
-// `GraphAdjacencyIndex`, `HNSWIndex`, `EntityIdMapper`, `UnifiedCache`)
+// `GraphAdjacencyIndex`, `JsHnswVectorIndex`, `EntityIdMapper`, `UnifiedCache`)
 // implement them too, so the contract can never silently diverge from the
 // thing Brainy ships.
 //
@@ -281,11 +281,11 @@ export interface CacheProvider {
  * connection lists as compact delta-varint byte sequences (cortex's
  * `encodeConnections` / `decodeConnections`).
  *
- * Brainy's `HNSWIndex` consumes this via a `ConnectionsCodec` that translates
+ * Brainy's `JsHnswVectorIndex` consumes this via a `ConnectionsCodec` that translates
  * UUIDs to stable int slots via the `EntityIdMapper`, encodes, and persists
  * the compressed bytes through the binary-blob primitive. On load, the blob
  * is fetched + decoded back into UUID sets — `setConnectionsCodec()` on
- * `HNSWIndex` is the injection point. Read path is dual-format: when no blob
+ * `JsHnswVectorIndex` is the injection point. Read path is dual-format: when no blob
  * exists for a node, the connections fall back to the legacy JSON-array path
  * embedded in `saveHNSWData`, so pre-2.4.0 indexes keep loading unchanged
  * and convergence to the compressed form happens lazily on next save.
@@ -304,7 +304,7 @@ export interface GraphCompressionProvider {
 
 /**
  * The `'vectorStore:mmap'` provider — a static factory class for an mmap-backed
- * vector file. Brainy's HNSWIndex uses the static `.create()` / `.open()`
+ * vector file. Brainy's JsHnswVectorIndex uses the static `.create()` / `.open()`
  * factories to open a single-file store at a derived path on disk-resident
  * storage adapters; non-FS adapters with no local-path support skip the mmap
  * layer and fall back to per-entity vector reads.
@@ -325,7 +325,7 @@ export interface VectorStoreMmapProvider {
 }
 
 /**
- * An open mmap-vector-store instance — the surface brainy's HNSWIndex consumes
+ * An open mmap-vector-store instance — the surface brainy's JsHnswVectorIndex consumes
  * for batch vector reads + lazy migration from per-entity storage on miss.
  */
 export interface VectorStoreMmapInstance {