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

public/images/favicon-no-bg.svg

@@ -0,0 +1,7 @@
+<svg width="166" height="166" viewBox="0 0 166 166" fill="none" xmlns="http://www.w3.org/2000/svg">
+<g transform="translate(40, 0)">
+<path d="M56.7848 80.9116L0 25.6211L24.8434 1.43151C26.8037 -0.47717 29.9814 -0.47717 31.9414 1.43151L85.177 53.2662L56.7848 80.9116Z" fill="#A5B4FC"/>
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+</g>
+</svg>

public/images/favicon.svg

@@ -1,7 +1,7 @@
 <svg width="166" height="166" viewBox="0 0 166 166" fill="none" xmlns="http://www.w3.org/2000/svg">
-<!-- Background -->
-<rect width="166" height="166" fill="rgb(38, 45, 59)"/>
-<g transform="translate(40, 0)">
+<!-- Circular Background -->
+<circle cx="83" cy="83" r="83" fill="#111827"/>
+<g transform="translate(48, 12) scale(0.85)">
 <path d="M56.7848 80.9116L0 25.6211L24.8434 1.43151C26.8037 -0.47717 29.9814 -0.47717 31.9414 1.43151L85.177 53.2662L56.7848 80.9116Z" fill="#A5B4FC"/>
 <path d="M-1.30805e-05 80.7335L21.2939 101.467L42.5878 80.7335L21.2939 60L-1.30805e-05 80.7335Z" fill="#E0E7FF"/>
 <path d="M56.7848 83L81.6279 107.19C83.5881 109.098 83.5881 112.192 81.6279 114.101L28.3925 165.936L0 138.29L56.7848 83Z" fill="#6366F1"/>