Add Architecture Workflow extension to community catalog (#2565)

Add arch extension submitted by @bigsmartben to:
- extensions/catalog.community.json (alphabetical order)
- docs/community/extensions.md community extensions table

Closes #2556

docs/community/extensions.md

@@ -28,6 +28,7 @@ The following community-contributed extensions are available in [`catalog.commun
 | API Evolve | Managed API contract evolution — breaking-change detection, semver enforcement, deprecation orchestration, and lifecycle gates across REST, GraphQL, and gRPC | `process` | Read+Write | [spec-kit-api-evolve](https://github.com/Quratulain-bilal/spec-kit-api-evolve) |
 | Architect Impact Previewer | Predicts architectural impact, complexity, and risks of proposed changes before implementation. | `visibility` | Read-only | [spec-kit-architect-preview](https://github.com/UmmeHabiba1312/spec-kit-architect-preview) |
 | Architecture Guard | Continuous architecture governance for AI-assisted development. Reviews specs, plans, and code for architecture drift, producing structured refactor tasks and evolution proposals. | `process` | Read+Write | [spec-kit-architecture-guard](https://github.com/DyanGalih/spec-kit-architecture-guard) |
+| Architecture Workflow | Generate project-level 4+1 architecture view artifacts and synthesis | `docs` | Read+Write | [spec-kit-arch](https://github.com/bigsmartben/spec-kit-arch) |
 | Archive Extension | Archive merged features into main project memory. | `docs` | Read+Write | [spec-kit-archive](https://github.com/stn1slv/spec-kit-archive) |
 | Azure DevOps Integration | Sync user stories and tasks to Azure DevOps work items using OAuth authentication | `integration` | Read+Write | [spec-kit-azure-devops](https://github.com/pragya247/spec-kit-azure-devops) |
 | Blueprint | Stay code-literate in AI-driven development: review a complete code blueprint for every task from spec artifacts before /speckit.implement runs | `docs` | Read+Write | [spec-kit-blueprint](https://github.com/chordpli/spec-kit-blueprint) |

extensions/catalog.community.json

@@ -174,6 +174,37 @@
       "created_at": "2026-05-07T00:00:00Z",
       "updated_at": "2026-05-07T00:00:00Z"
     },
+    "arch": {
+      "name": "Architecture Workflow",
+      "id": "arch",
+      "description": "Generate project-level 4+1 architecture view artifacts and synthesis",
+      "author": "bigsmartben",
+      "version": "1.0.0",
+      "download_url": "https://github.com/bigsmartben/spec-kit-arch/archive/refs/tags/v1.0.0.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",
+      "changelog": "https://github.com/bigsmartben/spec-kit-arch/blob/main/CHANGELOG.md",
+      "license": "MIT",
+      "requires": {
+        "speckit_version": ">=0.8.10.dev0"
+      },
+      "provides": {
+        "commands": 1,
+        "hooks": 0
+      },
+      "tags": [
+        "architecture",
+        "4plus1",
+        "workflow",
+        "design"
+      ],
+      "verified": false,
+      "downloads": 0,
+      "stars": 0,
+      "created_at": "2026-05-14T00:00:00Z",
+      "updated_at": "2026-05-14T00:00:00Z"
+    },
     "architect-preview": {
       "name": "Architect Impact Previewer",
       "id": "architect-preview",