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.

package.json

@@ -86,6 +86,7 @@
     "blob-stream": "^0.1.3",
     "bwip-js": "^4.8.0",
     "cropperjs": "^1.6.2",
+    "diff": "^8.0.3",
     "embedpdf-snippet": "file:vendor/embedpdf/embedpdf-snippet-2.3.0.tgz",
     "heic2any": "^0.0.4",
     "highlight.js": "^11.11.1",
@@ -111,11 +112,13 @@
     "markdown-it-task-lists": "^2.1.1",
     "markdown-it-toc-done-right": "^4.2.0",
     "mermaid": "^11.12.3",
+    "microdiff": "^1.5.0",
     "node-forge": "^1.3.3",
     "papaparse": "^5.5.3",
     "pdf-lib": "^1.17.1",
     "pdfjs-dist": "^5.4.624",
     "pdfkit": "^0.17.2",
+    "pixelmatch": "^7.1.0",
     "postal-mime": "^2.7.3",
     "rete": "^2.0.6",
     "rete-area-plugin": "^2.1.5",