docs: fix plugin count inconsistency in impact table

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

docs/DESIGN_CORE_REFACTOR.md

@@ -43,7 +43,7 @@ This document proposes **decomposing `@objectql/core`** from a monolithic runtim
 |--------|--------|-------|
 | `@objectql/core` LOC | ~3,500 | ~800 (thin re-exports + plugin orchestrator) |
 | Duplication with upstream | High (CRUD, hooks, middleware, repository, protocol) | Near-zero |
-| Plugin count (new) | 0 dedicated | 3 new plugins extracted |
+| Plugin count (new) | 0 dedicated | 4 new plugins extracted |
 | Upstream PRs needed | 0 | 3-4 PRs to `@objectstack/spec` |
 
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