🔒 Fix insecure randomness in TrinityKeystore cryptographic salt generation

[jason420247]

🎯 What:
Replaced Math.random() with crypto.getRandomValues() via Web Crypto API in TrinityKeystore.getVector() within App.tsx.

⚠️ Risk:
Math.random() is a pseudo-random number generator (PRNG) that is predictable and cryptographically insecure. Using it for generating cryptographic salts in keystore vectors can allow attackers to predict salt values and compromise key derivation or security parity.

🛡️ Solution:
Implemented cryptographically secure random value generation using window.crypto or globalThis.crypto's getRandomValues() method, ensuring secure entropy for cryptographic salts. Added proper error handling if a CSPRNG is unavailable in the execution context.

---

PR created automatically by Jules for task 9782411154547715725 started by @jason420247

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.