feat(core): add AntflyVectorStore implementation

New vector store backed by Antfly, replacing LanceDB + @xenova/transformers:
- Implements VectorStore interface with antfly SDK
- searchText() for hybrid search (BM25 + vector + RRF)
- Direct key lookup via tables.lookup() (replaces O(n) zero-vector hack)
- Auto-embedding on insert via Termite (embeddings param ignored)
- Batch insert in chunks of 500
- Model mismatch detection on initialize
- getModelInfo() and getStorageSize() for VectorStats
- searchByDocumentId() uses text-based similarity
- Typed SDK boundary layer (no any leakage)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: prosdev

packages/core/package.json

@@ -37,6 +37,7 @@
     "typescript": "^5.3.3"
   },
   "dependencies": {
+    "@antfly/sdk": "0.0.14",
     "@lancedb/lancedb": "^0.22.3",
     "@prosdevlab/dev-agent-types": "workspace:*",
     "@prosdevlab/kero": "workspace:*",