feat: add translation-sync reusable workflow

[DeepDiver1975]

Summary

Adds a reusable translation-sync workflow that can be called from any ownCloud app repository to sync translations with Transifex. Uses a GitHub App token for pull request creation so that created pull requests trigger workflows and commits are signed and attributed to the bot identity rather than github-actions[bot].

Inputs

Input	Required	Default	Description
mode	yes	—	old, make, or native
branch	no	master	Branch to open the translations pull request against
sub_path	no	l10n	Path within the repo where translation files live (e.g. l10n or .)
package_manager	no	npm	npm or pnpm (make mode only)

Secrets

Secret	Description
TX_TOKEN	Transifex API token
TRANSLATION_APP_ID	GitHub App ID used to open translation pull requests
TRANSLATION_APP_PRIVATE_KEY	GitHub App private key

Pull request behaviour

• A fixed branch name (chore/translations-update) means an open pull request is reused on subsequent sync runs rather than opening duplicates
• Merging deletes the branch; a fresh pull request is opened on the next run with changes
• No changes → no pull request created or updated
• Commits are signed via peter-evans/create-pull-request sign-commits: true
• Pull request creation is gated to the target branch, so workflow triggers on other refs only exercise the translation steps

Example caller

jobs:
  sync:
    uses: owncloud/reusable-workflows/.github/workflows/translation-sync.yml@main
    with:
      mode: old
      sub_path: l10n
    secrets:
      TX_TOKEN: ${{ secrets.TX_TOKEN }}
      TRANSLATION_APP_ID: ${{ secrets.TRANSLATION_APP_ID }}
      TRANSLATION_APP_PRIVATE_KEY: ${{ secrets.TRANSLATION_APP_PRIVATE_KEY }}

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