feat(l10n): add TRANSLATORS hints for footer, SMS and PDFtk

[lfals]

Resolves: #973

📝 Summary

Adds 20 // TRANSLATORS comments for PHP strings across LibreSign footer stamping, signer SMS/gateway notifications, Activity settings, admin settings section naming, and PDFtk administration overview checks:

• lib/Handler/FooterHandler.php
• lib/Listener/TwofactorGatewayListener.php
• lib/Handler/PdfTk/Pdf.php
• lib/Activity/Settings/FileSigned.php
• lib/Activity/Settings/FileToSign.php
• lib/Activity/Settings/SignRequestCanceled.php
• lib/Settings/AdminSettings.php
• lib/SetupCheck/PDFtkSetupCheck.php

Hints give LibreSign context for translators without changing English source strings. This is a 20-hint batch for #973.

Comments will appear in Transifex after the next extraction sync.

🧪 How to test

1. Review the files listed above and confirm each changed $this->l10n->t(...) / $this->l->t(...) has a // TRANSLATORS comment on the line above.
2. Confirm the diff is comments only — no English source strings changed.
3. Optional:
   • Open Nextcloud Administration settings → Overview and confirm PDFtk LibreSign messages still render the same English text.
   • Open Personal settings → Activity and confirm LibreSign activity setting labels still look the same.

⚙️ API / Back‑end changes

• Added PHP TRANSLATORS hints for footer defaults, Twofactor Gateway messages, Activity settings, admin section name, and PDFtk setup-check strings
• Unit and/or integration tests added – N/A: comment-only change; no behavior change
• Capabilities updated (if applicable)
• Documentation updated (if applicable)
• API documentation updated with composer openapi – N/A

✅ Checklist

• I have read and followed the contribution guide.
• Scoped to about 20 PHP translation hints as a follow-up batch of Implement translation hints in PHP #973
• No runtime behavior or source strings changed
• Conventional commit type uses an allowed prefix (feat)

🤖 AI (if applicable)

• The content of this PR was partially or fully generated using AI

Made with Cursor

[vitormattos]

/backport to stable34

[vitormattos]

/backport to stable33

[vitormattos]

/backport to stable32