Make Pixel bot's document map configurable by admin

[yiilinzhang]

Problem

The document map used by the RAG chatbot pipeline is currently hardcoded as a static JSON file at priv/course_documents/document_map.json. Any changes to the document catalogue (adding new lectures, exams, studios, etc.) require a code change and redeployment.

Proposed Solution

Allow admins to upload a CSV file through the admin panel to update the document map dynamically, without needing to modify source code.

Requirements

• Upload endpoint — Add a new admin API endpoint (e.g. PUT /courses/:course_id/admin/config/pixelbot_document_map) that accepts a CSV file upload.
• Validation — Validate the uploaded file against the expected schema (id, title, description, doc_type, year, week, s3_key) before persisting. Then convert the CSV into JSON for storage.
• Storage — Persist the document map to the database (rather than the filesystem) so it survives deployments and is course-scoped.
• Cache invalidation — Invalidate the persistent_term cache in Cadet.Chatbot.CourseDocuments when a new map is uploaded so the RAG pipeline picks up changes immediately.
• Frontend upload UI — Update PixelbotConfigPanel to include a file upload control (CSV) alongside the existing read-only document map display.

Relevant Files

• backend/priv/course_documents/document_map.json — current hardcoded map
• backend/lib/cadet/chatbot/course_documents.ex — loads and caches the map
• backend/lib/cadet_web/admin_controllers/admin_courses_controller.ex — existing get_document_map endpoint
• frontend/src/pages/academy/adminPanel/subcomponents/PixelbotConfigPanel.tsx — admin UI

Accepted Formats

Format	Notes
CSV	Header row matching the field names above