Initial commit: plugin repository structure

- GitHub Actions workflows for signing and validation
- Example file-manager plugin
- Scripts for batch signing

.github/workflows/validate.yml

@@ -0,0 +1,16 @@
+name: Validate PR
+
+on:
+  pull_request:
+    branches: [main]
+    paths:
+      - 'plugins/**'
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Validate manifests
+        run: bash scripts/validate.sh