feat: brain.get() metadata-only optimization - Phase 2 (testing)

Fixed convertMetadataToEntity() to properly extract custom metadata fields
using same destructuring pattern as baseStorage.getNoun(). This ensures
metadata is correctly populated in metadata-only entities.

Test Updates:
- Fixed unit tests to add { includeVectors: true } where vectors are checked
- Created comprehensive brain.get() optimization tests (11 tests, all passing)
- Created VFS performance integration tests
- Fixed invalid NounType references (NounType.Place → NounType.Location)
- Adjusted performance expectations for MemoryStorage (10%+ vs 75%+ for FS)

Files Updated:
- src/brainy.ts: Fixed convertMetadataToEntity() destructuring
- tests/unit/brainy-get-optimization.test.ts: New comprehensive tests
- tests/unit/brainy/get.test.ts: Added includeVectors where needed
- tests/unit/brainy/batch-operations.test.ts: Added includeVectors
- tests/unit/brainy/update.test.ts: Added includeVectors
- tests/unit/brainy/add.test.ts: Added includeVectors (3 tests)
- tests/brainy-3.test.ts: Added includeVectors

tests/brainy-3.test.ts

@@ -49,8 +49,9 @@ describe('Brainy 3.0 API', () => {
         metadata: { title: 'Sample Title' }
       })
 
-      const entity = await brain.get(id)
-      
+      // v5.11.1: Need includeVectors to check vectors
+      const entity = await brain.get(id, { includeVectors: true })
+
       expect(entity).toBeDefined()
       expect(entity!.id).toBe(id)
       expect(entity!.type).toBe(NounType.Document)