Document KB_BULK_SAFETY_PERCENT in README, DEVELOPER, MCP, and SKILL docs

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

DEVELOPER.md

@@ -94,6 +94,9 @@ All endpoints are under `/api/v1/`. Requires `Authorization: Bearer <key>` heade
 | `GET` | `/tags` | List all tags |
 | `GET` | `/status` | Engine status, GPU info, DB stats |
 | `POST` | `/reindex` | Re-embed all chunks |
+| `POST` | `/bulk/delete` | Bulk delete documents by filter |
+| `POST` | `/bulk/tags` | Bulk add/remove tags by filter |
+| `POST` | `/bulk/set-tags` | Bulk replace tags by filter |
 
 ## Future: ROCm runtime migration