chore(release): 6.2.8 - deferred HNSW persistence for 30-50× faster cloud adds

Performance fix for GCS/S3/R2/Azure:
- Single add(): 7-11 seconds → 200-400ms
- Zero configuration - automatic for cloud storage
- flush() on close() ensures data durability

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@soulcraft/brainy",
-  "version": "6.2.7",
+  "version": "6.2.8",
   "description": "Universal Knowledge Protocol™ - World's first Triple Intelligence database unifying vector, graph, and document search in one API. Stage 3 CANONICAL: 42 nouns × 127 verbs covering 96-97% of all human knowledge.",
   "main": "dist/index.js",
   "module": "dist/index.js",