chore(ci): improve repository maintenance configuration

- Enable weekly Dependabot updates for GitHub Actions dependencies
- Consolidate duplicate Trivy scans into a single SARIF scan with exit-code gate
- Ignore macOS metadata and locally downloaded drone-ssh binaries
- Add feature request issue template and pull request checklist template

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    labels:
+      - "dependencies"
+    commit-message:
+      prefix: "chore(ci)"