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/brainy.ts

@@ -9285,8 +9285,11 @@ export class Brainy<T = any> implements BrainyInterface<T> {
       reservedQueryMemory: config?.reservedQueryMemory ?? undefined as any,
       // HNSW persistence mode - undefined = smart default in setupIndex
       hnswPersistMode: config?.hnswPersistMode ?? undefined as any,
-      // HNSW optimization options (v7.11.0)
+      // HNSW optimization options (v7.11.0) — deprecated in 8.0, see `vector` below.
       hnsw: config?.hnsw ?? undefined as any,
+      // Vector index configuration (8.0) — algorithm-neutral surface with
+      // `recall` preset. See BRAINY-8.0-RENAME-COORDINATION § A.2.
+      vector: config?.vector ?? undefined as any,
       // Embedding initialization - false = lazy init on first embed()
       eagerEmbeddings: config?.eagerEmbeddings ?? false,
       // Plugin configuration - undefined = auto-detect