[TASK] Migrate remaining repos to shared reusable workflows

[CybotTM]

Context

The TYPO3-Documentation org is centralizing GitHub Actions workflows into shared
reusable workflows in this repository. Initial PRs cover 4 repos:

• TYPO3CMS-Reference-CoreApi (#6414)
• TYPO3CMS-Tutorial-Editors (#258)
• TYPO3CMS-Tutorial-GettingStarted (#792)
• render-guides (#1196)

Remaining repos

The following repos still use inline workflows and should be migrated once the
initial batch is accepted and proven stable:

• TYPO3CMS-Reference-TCA — backport (broken m-kuhn/backport), test-documentation
• TYPO3CMS-Reference-Typoscript — backport (broken), test-documentation
• TYPO3CMS-Reference-ViewHelper — backport (broken), test-documentation
• TYPO3CMS-Tutorial-SitePackage — backport (broken), test-documentation
• TYPO3CMS-Guide-FrontendLocalization — backport (broken)
• blog_example — backport (broken)

Available shared workflows

Workflow	Purpose
reusable-backport.yml	Automated backporting via labels
reusable-test-documentation.yml	Docker-based documentation rendering test
reusable-apply-precommit.yml	Scheduled pre-commit whitespace fixes
reusable-php-quality.yml	PHP CS Fixer + PHPStan quality checks
reusable-php-tests.yml	PHP unit/integration test matrix
reusable-php-command.yml	Generic PHP + Composer + command runner
reusable-docs-render.yml	Python/Composer-based documentation rendering

Note: Workflows linked to relative paths are added by #2 and not yet on main.

Priority

The backport migration is most urgent — 6 repos still reference the broken
m-kuhn/backport@30b6e83 action (missing dist/index.js). Migrating to the
shared reusable-backport.yml fixes this.

Migration pattern

For each repo, replace inline workflow files with shared workflow calls:

# Before (inline)
jobs:
  backport:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@...
      - uses: m-kuhn/backport@30b6e83  # BROKEN

# After (shared)
jobs:
  backport:
    uses: TYPO3-Documentation/.github/.github/workflows/reusable-backport.yml@main