Add Charter extension to community catalog

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

Closes #3322

Assisted-by: GitHub Copilot (model: claude-sonnet-4.6, autonomous)
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

extensions/catalog.community.json

@@ -1,6 +1,6 @@
 {
   "schema_version": "1.0",
-  "updated_at": "2026-07-01T00:00:00Z",
+  "updated_at": "2026-07-06T00:00:00Z",
   "catalog_url": "https://raw.githubusercontent.com/github/spec-kit/main/extensions/catalog.community.json",
   "extensions": {
     "aide": {
@@ -670,6 +670,40 @@
       "created_at": "2026-04-11T18:00:00Z",
       "updated_at": "2026-04-11T18:00:00Z"
     },
+    "charter": {
+      "name": "Charter",
+      "id": "charter",
+      "description": "Compose modular project constitutions from shared fragment registries. Centralize governance rules, select per-project fragments, track upstream changes, and keep multi-project setups consistent.",
+      "author": "Fyloss",
+      "version": "0.3.1",
+      "download_url": "https://github.com/Fyloss/spec-kit-charter/archive/refs/tags/v0.3.1.zip",
+      "repository": "https://github.com/Fyloss/spec-kit-charter",
+      "homepage": "https://github.com/Fyloss/spec-kit-charter",
+      "documentation": "https://github.com/Fyloss/spec-kit-charter/tree/master/docs",
+      "changelog": "https://github.com/Fyloss/spec-kit-charter/blob/master/CHANGELOG.md",
+      "license": "MIT",
+      "category": "process",
+      "effect": "read-write",
+      "requires": {
+        "speckit_version": ">=0.11.9"
+      },
+      "provides": {
+        "commands": 5,
+        "hooks": 1
+      },
+      "tags": [
+        "constitution",
+        "governance",
+        "modular",
+        "fragments",
+        "registry"
+      ],
+      "verified": false,
+      "downloads": 0,
+      "stars": 0,
+      "created_at": "2026-07-06T00:00:00Z",
+      "updated_at": "2026-07-06T00:00:00Z"
+    },
     "ci-guard": {
       "name": "CI Guard",
       "id": "ci-guard",