Reorganize: Move all skills to skills/ folder

- Created skills/ directory
- Moved 272 skills to skills/ subfolder
- Kept agents/ at root level
- Kept installation scripts and docs at root level

Repository structure:
- skills/           - All 272 skills from skills.sh
- agents/           - Agent definitions
- *.sh, *.ps1       - Installation scripts
- README.md, etc.   - Documentation

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

skills/plugins/marketplaces/claude-plugins-official/.github/workflows/close-external-prs.yml

@@ -0,0 +1,47 @@
+name: Close External PRs
+
+on:
+  pull_request_target:
+    types: [opened]
+
+permissions:
+  pull-requests: write
+  issues: write
+
+jobs:
+  check-membership:
+    if: vars.DISABLE_EXTERNAL_PR_CHECK != 'true'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check if author has write access
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const author = context.payload.pull_request.user.login;
+
+            const { data } = await github.rest.repos.getCollaboratorPermissionLevel({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              username: author
+            });
+
+            if (['admin', 'write'].includes(data.permission)) {
+              console.log(`${author} has ${data.permission} access, allowing PR`);
+              return;
+            }
+
+            console.log(`${author} has ${data.permission} access, closing PR`);
+
+            await github.rest.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: context.payload.pull_request.number,
+              body: `Thanks for your interest! This repo only accepts contributions from Anthropic team members. If you'd like to submit a plugin to the marketplace, please submit your plugin [here](https://docs.google.com/forms/d/e/1FAIpQLSdeFthxvjOXUjxg1i3KrOOkEPDJtn71XC-KjmQlxNP63xYydg/viewform).`
+            });
+
+            await github.rest.pulls.update({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: context.payload.pull_request.number,
+              state: 'closed'
+            });