Update DocGuard — CDD Enforcement extension to v0.28.0 (#3115)

Update docguard extension submitted by @raccioly:
- extensions/catalog.community.json (version, download_url, updated_at)
- docs/community/extensions.md community extensions table (no changes needed)

Closes #3106

Assisted-by: GitHub Copilot (model: claude-sonnet-4.6, autonomous)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

extensions/catalog.community.json

@@ -1,6 +1,6 @@
 {
   "schema_version": "1.0",
-  "updated_at": "2026-06-22T00:00:00Z",
+  "updated_at": "2026-06-23T00:00:00Z",
   "catalog_url": "https://raw.githubusercontent.com/github/spec-kit/main/extensions/catalog.community.json",
   "extensions": {
     "aide": {
@@ -1006,8 +1006,8 @@
       "id": "docguard",
       "description": "Canonical-Driven Development enforcement. Validates, scores, and traces project documentation with automated checks, AI-driven workflows, and spec-kit hooks. One pinned runtime dependency; pure Node.js otherwise.",
       "author": "raccioly",
-      "version": "0.27.0",
+      "version": "0.28.0",
-      "download_url": "https://github.com/raccioly/docguard/releases/download/v0.27.0/spec-kit-docguard-v0.27.0.zip",
+      "download_url": "https://github.com/raccioly/docguard/releases/download/v0.28.0/spec-kit-docguard-v0.28.0.zip",
       "repository": "https://github.com/raccioly/docguard",
       "homepage": "https://www.npmjs.com/package/docguard-cli",
       "documentation": "https://github.com/raccioly/docguard/blob/main/extensions/spec-kit-docguard/README.md",
@@ -1043,7 +1043,7 @@
       "downloads": 0,
       "stars": 0,
       "created_at": "2026-03-13T00:00:00Z",
-      "updated_at": "2026-06-22T00:00:00Z"
+      "updated_at": "2026-06-23T00:00:00Z"
     },
     "doctor": {
       "name": "Project Health Check",