refactor(8.0): final cleanup — drop HnswProvider alias + config.hnsw + 'hnsw' surface (scaffold step 6)

Step 6 of the brainy 8.0 rename scaffolding. Removes every legacy 'hnsw'-
flavoured public name introduced as a compat shim in steps 1-5. The
algorithm-neutral surface is now the only surface.

REMOVED — PHASE A (type aliases)

src/plugin.ts
- Removed `export type HnswProvider = VectorIndexProvider` alias.
- Removed `export type DiskAnnProvider = VectorIndexProvider` alias.

src/index.ts
- Removed `export const HNSWIndex = JsHnswVectorIndex` alias.

src/types/brainy.types.ts
- Removed `BrainyStats.indexHealth.hnsw` field (the new `vector` field
  carries the same boolean).

src/brainy.ts
- `stats()` no longer emits the legacy `hnsw` field on `indexHealth`.

REMOVED — PHASE B (storage adapter rename, 8 adapters)

Repo-wide rename: `saveHNSWData` → `saveVectorIndexData` and
`getHNSWData` → `getVectorIndexData` across:

- src/storage/adapters/baseStorageAdapter.ts (abstract declarations)
- src/storage/adapters/fileSystemStorage.ts
- src/storage/adapters/gcsStorage.ts
- src/storage/adapters/r2Storage.ts
- src/storage/adapters/s3CompatibleStorage.ts
- src/storage/adapters/azureBlobStorage.ts
- src/storage/adapters/opfsStorage.ts
- src/storage/adapters/memoryStorage.ts
- src/storage/adapters/historicalStorageAdapter.ts
- src/brainy.ts (call sites)
- src/hnsw/hnswIndex.ts + src/hnsw/typeAwareHNSWIndex.ts (call sites)

The default-delegation wrappers added in scaffold step 4 are removed
(would have been duplicate declarations after the rename).

REMOVED — PHASE C (cache category 'hnsw')

src/utils/unifiedCache.ts
- Cache-category union narrowed from
    'hnsw' | 'vectors' | 'metadata' | 'embedding' | 'other'
  to
    'vectors' | 'metadata' | 'embedding' | 'other'
- typeAccessCounts, typeSizes, typeCounts, accessRatios, sizeRatios,
  and the fairness-check iterator all drop the 'hnsw' key.
- Per planning § 2.5: pre-8.0 'hnsw' cache entries are an in-memory
  category. Cache is rebuildable; entries naturally don't exist after
  a restart, so no migration path is needed.

src/hnsw/hnswIndex.ts
- 3 cache.set() call sites migrated from category 'hnsw' to 'vectors'.
- Cache key prefix `hnsw:vector:` → `vector:`.
- typeCounts/typeSizes/typeAccessCounts accessor renames
  `.hnsw` → `.vectors`.

tests/unit/utils/unifiedCache-eviction.test.ts
- Test fixtures updated: cache.set(..., 'hnsw', ...) → cache.set(..., 'vectors', ...).
- Stats assertion `stats.typeSizes.hnsw` → `stats.typeSizes.vectors`.

REMOVED — PHASE D (config.hnsw)

src/types/brainy.types.ts
- Removed `BrainyConfig.hnsw` field entirely. The 8.0 surface is
  `BrainyConfig.vector.{recall, quantization, vectorStorage, advanced}`.

src/brainy.ts
- normalizeConfig() no longer emits a `hnsw` field on Required<BrainyConfig>.
- setupIndex() rewired:
  - Reads from `this.config.vector` (not `this.config.hnsw`).
  - Calls `resolveJsHnswConfig(this.config.vector)` to translate the
    `recall` preset into M / efConstruction / efSearch knobs (with
    `advanced.hnsw` overrides winning when supplied).
- Imports `resolveJsHnswConfig` from './utils/recallPreset.js'.

NOT IN THIS COMMIT (deliberately)

- Persisted file path migration `_system/hnsw-*.json` →
  `_system/vector-index-*.json`. Requires dual-read logic on boot
  across 8 storage adapters. Per integration doc lines 531-539:
  "Reader accepts either spelling on load; writer emits the new spelling
  only; brains self-migrate on the next persist after upgrade." This is
  a separate body of work and lands in a follow-up commit before 8.0 GA.
- `config.hnswPersistMode` top-level field is unchanged. It's not in
  the rename inventory; a future commit can fold it into
  `config.vector.persistMode` if desired.
- strictConfig enforcement wiring. The field is accepted by
  normalizeConfig() with default 'warn'; the actual warning emission at
  knob-mismatch sites lands when the config-resolution layer is touched
  for the persisted-path migration.

VERIFICATION

- npx tsc --noEmit: clean
- npm test: 1468 / 1468 unit (one test fixture updated to use the new
  category name; assertion still passes after fixture rename)
- npm run build: clean

The 8.0 PR's user-facing surface is now algorithm-neutral end-to-end:
VectorIndexProvider, config.vector.recall, JsHnswVectorIndex,
saveVectorIndexData, 'vectors' cache category, indexHealth.vector,
strictConfig — all standalone. No legacy 'hnsw' name remains in any
public type or method signature.

src/plugin.ts

@@ -221,23 +221,6 @@ export interface VectorIndexProvider {
   getPersistMode(): 'immediate' | 'deferred'
 }
 
-/**
- * @deprecated Renamed to {@link VectorIndexProvider} in Brainy 8.0. The
- * interface shape is byte-for-byte identical; only the name changed because
- * "vector index" describes the role, while "HNSW" was the name of one
- * specific implementation. This alias is provided as a compatibility shim
- * for code mid-migration; new code should import `VectorIndexProvider`.
- */
-export type HnswProvider = VectorIndexProvider
-
-/**
- * @deprecated The `'diskann'` provider key has been folded into `'vector'` in
- * Brainy 8.0. The vector index contract is implementation-neutral: any provider
- * registered under `'vector'` may be HNSW, DiskANN, or a future algorithm. The
- * type alias is preserved so existing imports compile while consumers migrate
- * to `VectorIndexProvider`.
- */
-export type DiskAnnProvider = VectorIndexProvider
 
 /**
  * The `'entityIdMapper'` provider — a drop-in for `EntityIdMapper`. Injected
@@ -265,10 +248,10 @@ export interface EntityIdMapperProvider {
  */
 export interface CacheProvider {
   getSync(key: string): any | undefined
-  set(key: string, data: any, type: 'hnsw' | 'metadata' | 'embedding' | 'other', size: number, rebuildCost?: number): void
+  set(key: string, data: any, type: 'vectors' | 'metadata' | 'embedding' | 'other', size: number, rebuildCost?: number): void
   delete(key: string): boolean
   deleteByPrefix(prefix: string): number
-  clear(type?: 'hnsw' | 'metadata' | 'embedding' | 'other'): void
+  clear(type?: 'vectors' | 'metadata' | 'embedding' | 'other'): void
 }
 
 // The `'embeddings'` / `'embedBatch'` providers are function-shaped and already
@@ -287,7 +270,7 @@ export interface CacheProvider {
  * is fetched + decoded back into UUID sets — `setConnectionsCodec()` on
  * `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
+ * embedded in `saveVectorIndexData`, so pre-2.4.0 indexes keep loading unchanged
  * and convergence to the compressed form happens lazily on next save.
  *
  * Activated only when the storage adapter exposes the binary-blob primitive