refactor(8.0): add config.vector path + 'vectors' cache category (scaffold step 2)

Step 2 of the brainy 8.0 rename scaffolding. Adds the new algorithm-neutral
config surface alongside the legacy config.hnsw path (which becomes a compat
shim removed in the final cleanup commit).

CHANGES

src/utils/recallPreset.ts (NEW)
- DEFAULT_RECALL = 'balanced'
- HNSW_PRESETS table — fast/balanced/accurate → (M, efConstruction, efSearch).
  'balanced' equals brainy 7.x DEFAULT_CONFIG byte-for-byte so a 7.x → 8.0
  upgrade with no explicit recall value is a no-op.
- resolveRecallHnswKnobs(preset) — preset → knobs.
- resolveJsHnswConfig(vectorConfig) — preset first, then `advanced.hnsw` overrides
  win. Explicit knobs always beat the preset.

src/types/brainy.types.ts
- New optional `vector` field on BrainyConfig:
    vector?: {
      recall?: 'fast' | 'balanced' | 'accurate'
      quantization?: { enabled?, bits?: 8 | 4, rerankMultiplier? }
      vectorStorage?: 'memory' | 'lazy'
      advanced?: {
        hnsw?: { M?, efConstruction?, efSearch?, ml? }
        diskann?: { pqM?, pqKsub?, maxDegree?, searchListSize?, alpha?, ... }
      }
    }
- `hnsw` field marked @deprecated with note that it stays as a compat shim
  during the 8.0 rename and is removed in the final cleanup commit.

src/utils/unifiedCache.ts
- Cache-category union widened from
    'hnsw' | 'metadata' | 'embedding' | 'other'
  to
    'hnsw' | 'vectors' | 'metadata' | 'embedding' | 'other'
- 5 union sites + 4 typed-counter maps (typeAccessCounts, checkFairness
  typeSizes/typeCounts/accessRatios/sizeRatios, getStats typeSizes/typeCounts,
  evictType loop) all gained the 'vectors' key with initial value 0.
- The hard-coded fairness-check loop now iterates both keys.
- Final 8.0 cleanup will narrow back to 'vectors' | 'metadata' | 'embedding' | 'other'.

src/brainy.ts (normalizeConfig)
- Adds the new `vector` field to the Required<BrainyConfig> return shape so
  TS compiles. Reads config?.vector ?? undefined as any (same pattern as
  the other optional config fields).

NO-OP scope

No behavioural change. The new config.vector path is silently ignored at
runtime in this commit — wired up in step 4 (storage + index resolution).
Pure surface plumbing. Tests + build green.

VERIFICATION

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

src/utils/unifiedCache.ts

@@ -21,7 +21,7 @@ import type { CacheProvider } from '../plugin.js'
 
 export interface CacheItem {
   key: string
-  type: 'hnsw' | 'metadata' | 'embedding' | 'other'
+  type: 'hnsw' | 'vectors' | 'metadata' | 'embedding' | 'other'
   data: any
   size: number
   rebuildCost: number  // milliseconds to rebuild
@@ -69,7 +69,7 @@ export class UnifiedCache implements CacheProvider {
   private cache = new Map<string, CacheItem>()
   private access = new Map<string, number>()  // Access counts
   private loadingPromises = new Map<string, Promise<any>>()
-  private typeAccessCounts = { hnsw: 0, metadata: 0, embedding: 0, other: 0 }
+  private typeAccessCounts = { hnsw: 0, vectors: 0, metadata: 0, embedding: 0, other: 0 }
   private totalAccessCount = 0
   private currentSize = 0
   private maxSize: number
@@ -209,7 +209,7 @@ export class UnifiedCache implements CacheProvider {
   set(
     key: string,
     data: any,
-    type: 'hnsw' | 'metadata' | 'embedding' | 'other',
+    type: 'hnsw' | 'vectors' | 'metadata' | 'embedding' | 'other',
     size: number,
     rebuildCost: number = 1
   ): void {
@@ -323,8 +323,8 @@ export class UnifiedCache implements CacheProvider {
 
   private checkFairness(): void {
     // Calculate type ratios in cache
-    const typeSizes = { hnsw: 0, metadata: 0, embedding: 0, other: 0 }
-    const typeCounts = { hnsw: 0, metadata: 0, embedding: 0, other: 0 }
+    const typeSizes = { hnsw: 0, vectors: 0, metadata: 0, embedding: 0, other: 0 }
+    const typeCounts = { hnsw: 0, vectors: 0, metadata: 0, embedding: 0, other: 0 }
 
     for (const item of this.cache.values()) {
       typeSizes[item.type] += item.size
@@ -335,6 +335,7 @@ export class UnifiedCache implements CacheProvider {
     const totalAccess = this.totalAccessCount || 1
     const accessRatios = {
       hnsw: this.typeAccessCounts.hnsw / totalAccess,
+      vectors: this.typeAccessCounts.vectors / totalAccess,
       metadata: this.typeAccessCounts.metadata / totalAccess,
       embedding: this.typeAccessCounts.embedding / totalAccess,
       other: this.typeAccessCounts.other / totalAccess
@@ -344,6 +345,7 @@ export class UnifiedCache implements CacheProvider {
     const totalSize = this.currentSize || 1
     const sizeRatios = {
       hnsw: typeSizes.hnsw / totalSize,
+      vectors: typeSizes.vectors / totalSize,
       metadata: typeSizes.metadata / totalSize,
       embedding: typeSizes.embedding / totalSize,
       other: typeSizes.other / totalSize
@@ -351,7 +353,7 @@ export class UnifiedCache implements CacheProvider {
 
     // Check for starvation (more aggressive - 70% cache with <15% accesses)
     // Previous: 90% cache, <10% access (too lenient, caused thrashing)
-    for (const type of ['hnsw', 'metadata', 'embedding', 'other'] as const) {
+    for (const type of ['hnsw', 'vectors', 'metadata', 'embedding', 'other'] as const) {
       if (sizeRatios[type] > 0.7 && accessRatios[type] < 0.15) {
         prodLog.warn(`Type ${type} is hogging cache (${(sizeRatios[type] * 100).toFixed(1)}% size, ${(accessRatios[type] * 100).toFixed(1)}% access)`)
         this.evictType(type)
@@ -364,7 +366,7 @@ export class UnifiedCache implements CacheProvider {
    * Called immediately when adding items to prevent imbalance formation
    * Uses same thresholds as periodic check but runs on-demand
    */
-  private checkProactiveFairness(addedType: 'hnsw' | 'metadata' | 'embedding' | 'other'): void {
+  private checkProactiveFairness(addedType: 'hnsw' | 'vectors' | 'metadata' | 'embedding' | 'other'): void {
     // Quick check: only evaluate the type being added
     let typeSize = 0
     for (const item of this.cache.values()) {
@@ -386,7 +388,7 @@ export class UnifiedCache implements CacheProvider {
   /**
    * Force evict items of a specific type
    */
-  private evictType(type: 'hnsw' | 'metadata' | 'embedding' | 'other'): void {
+  private evictType(type: 'hnsw' | 'vectors' | 'metadata' | 'embedding' | 'other'): void {
     const candidates: Array<[string, number, CacheItem]> = []
 
     for (const [key, item] of this.cache) {
@@ -466,7 +468,7 @@ export class UnifiedCache implements CacheProvider {
   /**
    * Clear cache or specific type
    */
-  clear(type?: 'hnsw' | 'metadata' | 'embedding' | 'other'): void {
+  clear(type?: 'hnsw' | 'vectors' | 'metadata' | 'embedding' | 'other'): void {
     if (!type) {
       this.cache.clear()
       this.currentSize = 0
@@ -533,8 +535,8 @@ export class UnifiedCache implements CacheProvider {
    * Get cache statistics with memory information
    */
   getStats() {
-    const typeSizes = { hnsw: 0, metadata: 0, embedding: 0, other: 0 }
-    const typeCounts = { hnsw: 0, metadata: 0, embedding: 0, other: 0 }
+    const typeSizes = { hnsw: 0, vectors: 0, metadata: 0, embedding: 0, other: 0 }
+    const typeCounts = { hnsw: 0, vectors: 0, metadata: 0, embedding: 0, other: 0 }
 
     for (const item of this.cache.values()) {
       typeSizes[item.type] += item.size