chore: bump version to 5.8.0, update CHANGELOG

- Added [5.8.0] section documenting all projman hardening changes
- Updated README.md title to v5.8.0
- Updated marketplace.json version to 5.8.0

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": "5.7.1"
+    "version": "5.8.0"
   },
   "plugins": [
     {