refactor(8.0): simplify config.vector to 3 knobs + fold persistMode (scaffold step 8)

Per user direction and BRAINY-8.0-RENAME-COORDINATION § G.2: the
`config.vector.advanced.{hnsw, diskann}` escape-hatch surface was
over-engineered. The 8.0 config surface collapses to **three knobs**:

```
config.vector = {
  recall?: 'fast' | 'balanced' | 'accurate'
  quantization?: { enabled?, bits?: 8 | 4 }
  persistMode?: 'immediate' | 'deferred'
}
```

The algorithm-internal HNSW knobs (`M`, `efConstruction`, `efSearch`,
`ml`) and DiskANN knobs (`pqM`, `searchListSize`, `alpha`, …) are no
longer exposed at the public surface. The `recall` preset covers the
legitimate quality/latency tradeoff; algorithm-internal tuning is
intentionally hidden. If users need it later, we can add it back —
shipping with too few knobs is easier to evolve than shipping with too
many.

CHANGES

src/types/brainy.types.ts
- BrainyConfig.hnswPersistMode (7.x top-level) → BrainyConfig.vector.persistMode.
- BrainyConfig.vector — dropped `advanced.{hnsw, diskann}` sub-block.
- BrainyConfig.vector.quantization — dropped `rerankMultiplier` (hardcoded to 3).
- BrainyConfig.vector — dropped `vectorStorage: 'memory' | 'lazy'`. Brainy
  always keeps vectors resident in 8.0; the lazy-eviction path was a
  cloud-storage optimisation that's no longer needed (cloud adapters are gone).
- JSDoc tightened to reflect the closed-form contract.

src/utils/recallPreset.ts
- resolveJsHnswConfig() signature narrowed: accepts `{ recall? }` only
  (no more `advanced` parameter).

src/brainy.ts
- normalizeConfig() — no longer carries `hnswPersistMode` on the resolved
  config. Dropped the deprecated 'gcs-native' warning, the gcsStorage
  HMAC-key warning, and the lenient storage-pairing block (dead code now
  that cloud adapters are gone).
- resolveHNSWPersistMode() — collapsed to a one-liner:
  `return this.config.vector?.persistMode ?? 'immediate'`. The cloud-vs-local
  smart-default branching is no longer relevant (filesystem is the only
  persistent backend in 8.0).
- setupIndex() — reads quantization fields from config.vector directly;
  rerankMultiplier hardcoded to 3.

NO-OP scope

The recall preset's 'balanced' = brainy 7.x DEFAULT_CONFIG byte-for-byte,
so users who don't set recall get the same behavior. Users who set
config.hnsw.* in 7.x will need to migrate to config.vector.* per the
8.0 release notes; pure 7.x defaults users see no change.

VERIFICATION

- npx tsc --noEmit: clean
- npm test: 1408 / 1409 (same pre-existing test-isolation race condition
  from step 7, not related to step 8)

src/brainy.ts

@@ -9068,16 +9068,17 @@ export class Brainy<T = any> implements BrainyInterface<T> {
   }
 
   /**
-   * Setup index — single unified HNSW graph.
+   * Setup index — single unified vector graph.
    *
-   * Smart defaults for HNSW persistence mode:
-   * - Cloud storage (GCS/S3/R2/Azure): 'deferred' for 30-50x faster adds
-   * - Local storage (FileSystem/Memory/OPFS): 'immediate' (already fast)
+   * Brainy 8.0 ships filesystem-only storage (no cloud adapters), so persistence
+   * mode defaults to `'immediate'` everywhere. Operators who want bulk-ingest
+   * speed can set `config.vector.persistMode = 'deferred'`.
    */
   private setupIndex(): JsHnswVectorIndex {
-    // 8.0 config surface: config.vector.{quantization, vectorStorage, recall, advanced}.
-    // The recall preset translates to HNSW knobs (M / efConstruction / efSearch) via
-    // resolveJsHnswConfig; explicit advanced.hnsw overrides win.
+    // 8.0 config surface: config.vector.{recall, quantization, persistMode}.
+    // The recall preset translates to HNSW knobs (M / efConstruction / efSearch)
+    // via resolveJsHnswConfig. No algorithm-internal knobs are exposed at the
+    // public surface.
     const recallKnobs = resolveJsHnswConfig(this.config.vector)
     const vectorCfg = this.config.vector
     const indexConfig = {
@@ -9087,9 +9088,8 @@ export class Brainy<T = any> implements BrainyInterface<T> {
       quantization: vectorCfg?.quantization ? {
         enabled: vectorCfg.quantization.enabled ?? false,
         bits: vectorCfg.quantization.bits ?? 8,
-        rerankMultiplier: vectorCfg.quantization.rerankMultiplier ?? 3
-      } : undefined,
-      vectorStorage: vectorCfg?.vectorStorage
+        rerankMultiplier: 3
+      } : undefined
     }
 
     const persistMode = this.resolveHNSWPersistMode()
@@ -9211,49 +9211,28 @@ export class Brainy<T = any> implements BrainyInterface<T> {
    * Resolve HNSW persistence mode.
    * Extracted so both setupIndex() and the HNSW plugin factory path can use it.
    *
-   * User config > smart default:
-   * - Cloud storage (GCS/S3/R2/Azure): 'deferred' for 30-50x faster adds
-   * - Local storage (FileSystem/Memory/OPFS): 'immediate' (already fast)
+   * Brainy 8.0 ships filesystem-only; the cloud-storage smart-default
+   * (deferred for cloud, immediate for local) collapses to "always
+   * immediate unless the user overrides via config.vector.persistMode".
    */
   private resolveHNSWPersistMode(): 'immediate' | 'deferred' {
-    let persistMode: 'immediate' | 'deferred' = this.config.hnswPersistMode || 'immediate'
-
-    if (!this.config.hnswPersistMode) {
-      const storageType = this.config.storage?.type || this.getStorageType()
-      if (['gcs', 's3', 'r2', 'azure'].includes(storageType)) {
-        persistMode = 'deferred'
-      }
-    }
-
-    return persistMode
+    return this.config.vector?.persistMode ?? 'immediate'
   }
 
   /**
    * Normalize and validate configuration
    */
   private normalizeConfig(config?: BrainyConfig): Required<BrainyConfig> {
-    // Validate storage configuration
-    if (config?.storage?.type && !['auto', 'memory', 'filesystem', 'opfs', 'remote', 's3', 'r2', 'gcs', 'gcs-native', 'azure'].includes(config.storage.type)) {
-      throw new Error(`Invalid storage type: ${config.storage.type}. Must be one of: auto, memory, filesystem, opfs, remote, s3, r2, gcs, gcs-native, azure`)
-    }
-
-    // Warn about deprecated gcs-native
-    if (config?.storage?.type === ('gcs-native' as any)) {
-      console.warn('⚠️  DEPRECATED: type "gcs-native" is deprecated. Use type "gcs" instead.')
-      console.warn('   This will continue to work but may be removed in a future version.')
-    }
-
-    // Validate storage type/config pairing (now more lenient)
-    if (config?.storage) {
-      const storage = config.storage as any
-
-      // Warn about legacy gcsStorage config with HMAC keys
-      if (storage.gcsStorage && storage.gcsStorage.accessKeyId && storage.gcsStorage.secretAccessKey) {
-        console.warn('⚠️  GCS with HMAC keys (gcsStorage) is legacy. Consider migrating to native GCS (gcsNativeStorage) with ADC.')
-      }
-
-      // No longer throw errors for mismatches - storageFactory now handles this intelligently
-      // Both 'gcs' and 'gcs-native' can now use either gcsStorage or gcsNativeStorage
+    // Validate storage configuration. Brainy 8.0 ships two adapters only —
+    // FileSystemStorage and MemoryStorage — per BR-BRAINY-80-STORAGE-SIMPLIFY.
+    // Cloud backup remains supported via operator tooling (db.persist() +
+    // gsutil / aws s3 cp / rclone / azcopy).
+    if (config?.storage?.type && !['auto', 'memory', 'filesystem'].includes(config.storage.type)) {
+      throw new Error(
+        `Invalid storage type: ${config.storage.type}. Brainy 8.0 ships 'auto', 'memory', and 'filesystem' only. ` +
+          `Cloud storage adapters (GCS / S3 / R2 / Azure) and OPFS were removed in 8.0; ` +
+          `back up locally with db.persist() and sync the on-disk artefact with your tool of choice.`
+      )
     }
 
     // Validate numeric configurations
@@ -9292,10 +9271,9 @@ export class Brainy<T = any> implements BrainyInterface<T> {
       // Memory management options
       maxQueryLimit: config?.maxQueryLimit ?? undefined as any,
       reservedQueryMemory: config?.reservedQueryMemory ?? undefined as any,
-      // HNSW persistence mode - undefined = smart default in setupIndex
-      hnswPersistMode: config?.hnswPersistMode ?? undefined as any,
       // Vector index configuration (8.0) — algorithm-neutral surface with
-      // `recall` preset. See BRAINY-8.0-RENAME-COORDINATION § A.2.
+      // `recall` preset + `persistMode` (folded in from 7.x's hnswPersistMode).
+      // See BRAINY-8.0-RENAME-COORDINATION § A.2 + § G.2.
       vector: config?.vector ?? undefined as any,
       // Embedding initialization - false = lazy init on first embed()
       eagerEmbeddings: config?.eagerEmbeddings ?? false,