Refactor styles and implement new canvas viewport
- Updated styles in `styles.rs` to include new pane and canvas backgrounds, while marking unused functions with `#[allow(dead_code)]`. - Modified `text_editor.rs` to suppress warnings for unused function parameters. - Enhanced `title_bar.rs` to create a unified title/menu bar with improved hover states and draggable functionality. - Simplified `sidebar.rs` to always use a single-column layout and improved tool button styling with hover feedback. - Added a new `viewport.rs` file to implement a custom canvas viewport widget for zoom and pan rendering, replacing the previous layout-based approach. - Updated theme management in `theme.rs` to suppress warnings for unused methods. - Adjusted line count report to reflect recent changes in codebase.
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