Address review: use catalog.community.json and add extensions README

Per maintainer feedback:
- Revert catalog.json to its original empty state (empty by design)
- Rename catalog.example.json → catalog.community.json
- Replace example entries with real V-Model Extension Pack entry
- Add extensions/README.md with community extensions table

Author: leocamello

extensions/README.md

@@ -0,0 +1,13 @@
+# Spec Kit Community Extensions
+
+Community-contributed extensions for [Spec Kit](https://github.com/github/spec-kit).
+
+## Available Extensions
+
+| Extension | Purpose | URL |
+|-----------|---------|-----|
+| V-Model Extension Pack | Enforces V-Model paired generation of development specs and test specs with full traceability | [spec-kit-v-model](https://github.com/leocamello/spec-kit-v-model) |
+
+## Adding Your Extension
+
+See the [Extension Publishing Guide](EXTENSION-PUBLISHING-GUIDE.md) for instructions on how to submit your extension to the community catalog.

extensions/catalog.community.json

@@ -0,0 +1,33 @@
+{
+  "schema_version": "1.0",
+  "updated_at": "2026-02-20T00:00:00Z",
+  "catalog_url": "https://raw.githubusercontent.com/github/spec-kit/main/extensions/catalog.community.json",
+  "extensions": {
+    "v-model": {
+      "name": "V-Model Extension Pack",
+      "id": "v-model",
+      "description": "Enforces V-Model paired generation of development specs and test specs with full traceability.",
+      "author": "leocamello",
+      "version": "0.1.0",
+      "download_url": "https://github.com/leocamello/spec-kit-v-model/archive/refs/tags/v0.1.0.zip",
+      "repository": "https://github.com/leocamello/spec-kit-v-model",
+      "homepage": "https://github.com/leocamello/spec-kit-v-model",
+      "documentation": "https://github.com/leocamello/spec-kit-v-model/blob/main/README.md",
+      "changelog": "https://github.com/leocamello/spec-kit-v-model/blob/main/CHANGELOG.md",
+      "license": "MIT",
+      "requires": {
+        "speckit_version": ">=0.1.0"
+      },
+      "provides": {
+        "commands": 3,
+        "hooks": 1
+      },
+      "tags": ["v-model", "traceability", "testing", "compliance", "safety-critical"],
+      "verified": false,
+      "downloads": 0,
+      "stars": 0,
+      "created_at": "2026-02-20T00:00:00Z",
+      "updated_at": "2026-02-20T00:00:00Z"
+    }
+  }
+}

extensions/catalog.example.json

@@ -1,38 +1,6 @@
 {
   "schema_version": "1.0",
-  "updated_at": "2026-02-20T00:00:00Z",
+  "updated_at": "2026-02-03T00:00:00Z",
   "catalog_url": "https://raw.githubusercontent.com/github/spec-kit/main/extensions/catalog.json",
-  "extensions": {
-    "v-model": {
-      "name": "V-Model Extension Pack",
-      "id": "v-model",
-      "description": "Enforces V-Model paired generation of development specs and test specs with full traceability.",
-      "author": "leocamello",
-      "version": "0.1.0",
-      "download_url": "https://github.com/leocamello/spec-kit-v-model/archive/refs/tags/v0.1.0.zip",
-      "repository": "https://github.com/leocamello/spec-kit-v-model",
-      "license": "MIT",
-      "requires": {
-        "speckit_version": ">=0.1.0"
-      },
-      "provides": {
-        "commands": 3,
-        "hooks": 1
-      },
-      "tags": [
-        "v-model",
-        "traceability",
-        "testing",
-        "compliance",
-        "safety-critical"
-      ],
-      "verified": false,
-      "created_at": "2026-02-20T00:00:00Z",
-      "updated_at": "2026-02-20T00:00:00Z",
-      "statistics": {
-        "downloads": 0,
-        "stars": 0
-      }
-    }
-  }
+  "extensions": {}
 }