Upgrade GitHub Actions to Node.js 24 compatible versions and add single build workflow

[fvgfgtxdeujv]

Changes

1. Upgrade GitHub Actions to latest versions

• actions/checkout: v4 → v7
• actions/upload-artifact: v4 → v7
• actions/download-artifact: v4 → v8
• softprops/action-gh-release: v2 → v3

These versions natively support Node.js 24, resolving the deprecation warnings.

2. Add Node.js 24 support

• Added FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true environment variable to all workflows
• Ensures compatibility with the June 16, 2026 migration deadline

3. Add pull_request trigger

• build-rootfs-releases.yml now runs automatically on PRs to main
• cleanup-old-assets.yml remains manual-only (no PR trigger needed)

4. Switch to manual trigger for scheduled workflows

• Removed schedule trigger (weekly cron) from build-rootfs-releases.yml and cleanup-old-assets.yml
• Workflows now only run via workflow_dispatch or pull_request

5. Add single rootfs build workflow

• New build-single-rootfs.yml workflow
• Dropdown menu to select one of 14 templates
• Builds and uploads as artifact (7-day retention)
• Does not create GitHub Release

Motivation

• GitHub Actions deprecated Node.js 20 on June 16, 2026
• Previous action versions (v4) only support Node.js 20
• PR trigger enables automatic builds for code review
• Manual trigger provides better control over release timing
• Single build workflow allows quick testing of individual templates

Testing

• All workflows updated and tested