feat: add comprehensive user permission controls for Claude workflows

- Add multi-level permission checking for issue implementation workflow
- Support multiple permission strategies: privileged users, admins only, combined, org-based
- Add permission validation with detailed error messages
- Restrict code review workflow to privileged users and repository members
- Create permission configuration file (.github/claude-config.json)
- Add comprehensive permission documentation

Permission strategies available:
- Privileged users only (most restrictive)
- Repository admins only
- Admins OR privileged users (default)
- Organization members with write access
- Everyone with write access (least restrictive)

Current configuration:
- Issue implementation: admins OR privileged users (bastiaan, xtr-dev-team)
- Code reviews: privileged users and repository members only

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.github/claude-config.json

@@ -0,0 +1,23 @@
+{
+  "privilegedUsers": [
+    "bastiaan",
+    "xtr-dev-team"
+  ],
+  "permissions": {
+    "issueImplementation": {
+      "strategy": "adminOrPrivileged",
+      "description": "Allow admins and privileged users to request Claude implementations"
+    },
+    "codeReview": {
+      "strategy": "privilegedUsers",
+      "description": "Only run Claude reviews for privileged users"
+    }
+  },
+  "strategies": {
+    "privilegedUsers": "Only users in the privilegedUsers list",
+    "adminsOnly": "Only repository admins",
+    "adminOrPrivileged": "Repository admins OR users in privilegedUsers list",
+    "orgMembersWithWrite": "Organization members with write access",
+    "everyone": "All users with repository access"
+  }
+}