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

docs/.vitepress/config.mts

@@ -8,7 +8,7 @@ export default defineConfig({
 
     themeConfig: {
         // https://vitepress.dev/reference/default-theme-config
-        logo: '/images/favicon.svg',
+        logo: '/images/favicon-no-bg.svg',
 
         nav: [
             { text: 'Home', link: '/' },