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.

Cargo.toml

@@ -62,7 +62,7 @@ eframe      = { version = "0.34", default-features = false, features = ["default
 egui_extras = { version = "0.34", features = ["svg", "image"] }
 egui_dock   = { version = "0.19", features = ["serde"] }
 rfd         = "0.15"
-iced        = { version = "0.13", features = ["tokio", "image", "svg"] }
+iced        = { version = "0.13", features = ["tokio", "image", "svg", "canvas"] }
 
 # Utilities
 base64      = "0.22"