chore: prepare v1.51.6 release (#336)

* chore: bump plugin version to 1.51.6

* chore: add benchmark results for v1.51.6

Generated by CI benchmark workflow on chore/v1.51.6-release-prep

🤖 Generated automatically

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Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: erraggy

.claude-plugin/marketplace.json

@@ -10,7 +10,7 @@
     {
       "name": "oastools",
       "description": "15 MCP tools and 5 guided skills for working with OpenAPI specs — validate, fix, convert, diff, join, overlay, generate, and walk operations/schemas/parameters/responses/security/paths",
-      "version": "1.51.5",
+      "version": "1.51.6",
       "author": {
         "name": "erraggy",
         "url": "https://github.com/erraggy"