feat: add questionnaires admin UI

[kenzaelk98]

Summary

Adds an admin UI to list, create, edit, activate/close, duplicate, and delete questionnaires via LibreChat’s /api/admin/questionnaires API.

Depends on

danny-avila/LibreChat#15780 — needs the questionnaire admin API and read:questionnaires / manage:questionnaires capabilities.

Related: danny-avila/LibreChat#14643

What’s included

• Sidebar + routes for questionnaires list and editor
• Create/edit draft/active/closed rounds (one active at a time, enforced by the API)
• Editor options aligned with LibreChat: dismissible, permanent dismiss (repromptIntervalHours: null), showConfetti, thank-you message, schedule, questions
• Capability gating for read/manage questionnaires

Screenshots

Example Questionnaire Section

Example Questionnaire Editor

Change Type

• New feature (non-breaking change which adds functionality)
• Translation update

Test plan

• Run against a LibreChat instance that includes #15780
• Open Questionnaires in the admin panel (capabilities granted)
• Create a draft, add questions, save
• Activate (confirm previous active is closed by API)
• Toggle dismissible / permanent dismiss / confetti and save; confirm values round-trip
• Duplicate, finish (close), delete

Checklist

• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• My changes do not introduce new warnings