feat: add Random Generator tool

Cryptographically secure generator for 5 types:
- Password: configurable charset + entropy strength meter
- UUID: crypto.randomUUID()
- API Key: hex/base62/base64url with optional prefix
- Hash: SHA-1/256/512 of custom input or random data
- Token: variable byte-length in hex or base64url

All using Web Crypto API — nothing leaves the browser.
Registered in lib/tools.tsx with RandomIcon (dice).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/AppIcons.tsx

@@ -67,6 +67,17 @@ export const QRCodeIcon = (props: React.SVGProps<SVGSVGElement>) => (
   </svg>
 );
 
+export const RandomIcon = (props: React.SVGProps<SVGSVGElement>) => (
+  <svg {...props} fill="none" stroke="currentColor" viewBox="0 0 24 24">
+    <rect x="3" y="3" width="18" height="18" rx="3" strokeWidth={2} />
+    <circle cx="8.5" cy="8.5" r="1.25" fill="currentColor" stroke="none" />
+    <circle cx="15.5" cy="8.5" r="1.25" fill="currentColor" stroke="none" />
+    <circle cx="8.5" cy="15.5" r="1.25" fill="currentColor" stroke="none" />
+    <circle cx="15.5" cy="15.5" r="1.25" fill="currentColor" stroke="none" />
+    <circle cx="12" cy="12" r="1.25" fill="currentColor" stroke="none" />
+  </svg>
+);
+
 export const CalculateIcon = (props: React.SVGProps<SVGSVGElement>) => (
   <svg {...props} fill="none" stroke="currentColor" viewBox="0 0 24 24">
     {/* Y-axis */}