feat: add digital signature PDF tool

- Add new tool to apply cryptographic signatures to PDFs using X.509 certificates
- Support PKCS#12 (.pfx, .p12) and PEM certificate formats
- Create PKCS#7 detached signatures compatible with all major PDF viewers
- Optional visible signature with customizable position, image, and text overlay
- Add translations for English, German, Vietnamese, and Chinese

src/js/utils/full-width.ts

@@ -2,7 +2,7 @@
 // This script applies the full-width preference from localStorage to page uploaders
 
 export function initFullWidthMode() {
-    const savedFullWidth = localStorage.getItem('fullWidthMode') === 'true';
+    const savedFullWidth = localStorage.getItem('fullWidthMode') !== 'false';
 
     if (savedFullWidth) {
         applyFullWidthMode(true);