Add Highlight struct with SHA-256 hashing and improve query

- Add Highlight struct to represent bookmarks with owned memory
- Implement SHA-256 hashing for text and book identification
- Update SQL query to extract clean book filenames (removes path and fragment)
- Remove unused Annotation column from query
- Add CLAUDE.md for repository documentation
- Update .gitignore to exclude SQLite WAL files

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.gitignore

@@ -16,6 +16,8 @@ kb_exfiltrator-kobo-arm
 local-dev.sqlite
 *.sqlite
 *.db
+*.sqlite-shm
+*.sqlite-wal
 
 # Editor/IDE files
 .vscode/