chore: release v5.0.0

- Update version to 5.0.0 in README.md, marketplace.json, CLAUDE.md
- Convert [Unreleased] to [5.0.0] in CHANGELOG.md
- Add contract-validator to CANONICAL-PATHS.md

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -6,7 +6,7 @@
   },
   "metadata": {
     "description": "Project management plugins with Gitea and NetBox integrations",
-    "version": "4.1.0"
+    "version": "5.0.0"
   },
   "plugins": [
     {