Fix course editor: field mismatches, TinyMCE, AI without save
Backend fixes:
- Remove nonexistent fields: category, thumbnail_url, file_path, sort_order
- Map to actual model fields: thumbnail_path, local_file_path, position
- Add standalone AI content endpoint (no lesson save required)
- Add missing lesson fields to course detail response
Frontend fixes:
- Fix lesson_type (was "type"), live_session_url (was "live_url")
- Fix lesson save/delete URLs to match backend routes
- Add TinyMCE rich text editor for text lessons (self-hosted, GPL)
- AI Generate works before saving lesson (uses course-level endpoint)
- Proper input styling: larger padding, border-radius, consistent sizing
- Module title input properly styled
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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