Update Architecture Workflow extension to v1.2.1 (#3118)

Update arch extension submitted by @bigsmartben to:
- extensions/catalog.community.json (version, download_url, description, provides.commands)
- docs/community/extensions.md community extensions table

Closes #3111

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extensions/catalog.community.json

@@ -187,10 +187,10 @@
     "arch": {
       "name": "Architecture Workflow",
       "id": "arch",
-      "description": "Generate or reverse project-level 4+1 architecture view artifacts and synthesis",
+      "description": "Generate or reverse project-level 4+1 architecture views as separate commands",
       "author": "bigsmartben",
-      "version": "1.1.0",
-      "download_url": "https://github.com/bigsmartben/spec-kit-arch/archive/refs/tags/v1.1.0.zip",
+      "version": "1.2.1",
+      "download_url": "https://github.com/bigsmartben/spec-kit-arch/archive/refs/tags/v1.2.1.zip",
       "repository": "https://github.com/bigsmartben/spec-kit-arch",
       "homepage": "https://github.com/bigsmartben/spec-kit-arch",
       "documentation": "https://github.com/bigsmartben/spec-kit-arch/blob/main/README.md",
@@ -202,7 +202,7 @@
         "speckit_version": ">=0.8.10.dev0"
       },
       "provides": {
-        "commands": 2,
+        "commands": 10,
         "hooks": 0
       },
       "tags": [
@@ -215,7 +215,7 @@
       "downloads": 0,
       "stars": 0,
       "created_at": "2026-05-14T00:00:00Z",
-      "updated_at": "2026-05-15T00:00:00Z"
+      "updated_at": "2026-06-23T00:00:00Z"
     },
     "architect-preview": {
       "name": "Architect Impact Previewer",