refactor: update PDF comparison types and enhance UI for better usability

- Refactored CompareState to import from a centralized type definition.
- Enhanced the compare-pdfs.html layout with improved styles for overlay and side-by-side modes.
- Added new CSS styles for various UI components including panels, buttons, and highlights.
- Implemented a new sidebar for displaying change summaries and filters.
- Created unit tests for text comparison logic, including diffing text runs and page pairing.
- Added tests for text normalization functions to ensure proper handling of punctuation and character normalization.

src/css/styles.css

@@ -238,19 +238,6 @@ input[type='file']::file-selector-button {
   position: relative;
   width: 100%;
   height: 75vh;
-  overflow: auto;
-  border: 2px solid #374151;
-  border-radius: 0.5rem;
-  background-color: #1f2937;
-}
-
-/* This rule now ONLY applies to canvases in overlay mode */
-.compare-viewer-wrapper.overlay-mode canvas {
-  position: absolute;
-  top: 0;
-  left: 0;
-  width: 100%;
-  height: auto;
 }
 
 .compare-viewer-wrapper.side-by-side-mode {