docs: remove backward compatibility documentation sections

- Removed 'Ebook Compatibility (Backward Compatible)' section
- Removed 'Backward Compatibility Views' from database docs
- Removed backward compatibility bullet point from Database Schema section
- Cleaned up legacy API references from README

This is part of legacy code cleanup Phase 1.
Phase 1: Documentation Cleanup

README.md

@@ -176,18 +176,7 @@ POST /api/media-items/{id}/highlights                  # Create new highlight
 GET /api/media-items/{id}/highlights/{highlightId}      # Get specific highlight
 PUT /api/media-items/{id}/highlights/{highlightId}       # Update highlight
 DELETE /api/media-items/{id}/highlights/{highlightId}   # Delete highlight
-
-# Ebook Compatibility (Backward Compatible)
-GET /api/ebooks/{id}/notes              # Get user's notes for ebook
-POST /api/ebooks/{id}/notes             # Create new ebook note
-PUT /api/ebooks/{id}/notes/{noteId}    # Update ebook note
-DELETE /api/ebooks/{id}/notes/{noteId} # Delete ebook note
-
-GET /api/ebooks/{id}/highlights                   # Get user's highlights for ebook
-POST /api/ebooks/{id}/highlights                  # Create new ebook highlight
-PUT /api/ebooks/{id}/highlights/{highlightId}       # Update ebook highlight
-DELETE /api/ebooks/{id}/highlights/{highlightId}   # Delete ebook highlight
- ```
+  ```
 
 #### Media Search (All Authenticated Users)
 ```bash
@@ -363,7 +352,6 @@ The application automatically starts background services on startup:
 ### Database Schema
 - **Multi-Library Architecture**: Libraries, library types, folders, visibility tables
 - **Annotations System**: Notes, highlights with position tracking and color customization
-- **Backward Compatibility**: Views maintain existing API contracts for ebooks
 - **Type Safety**: pgx v5 with proper error handling
 - **Migration Ready**: Schema designed for easy future extensions
 
@@ -586,10 +574,6 @@ refresh_tokens        # JWT refresh token storage
 
 # Database Functions
 normalize_isbn()      # ISBN normalization function
-
-# Backward Compatibility Views
-ebook_notes           # Notes view for ebook API compatibility
-ebook_highlights      # Highlights view for ebook API compatibility
 ```
 
 ## 🎯 Future Roadmap