fix: replace crypto.randomUUID with compatible helper for HTTP contexts

[yuhp]

Description

This PR fixes a crash when accessing the application over a local network (LAN) via HTTP (e.g., http://192.168.1.x:3000).

The Issue

The native crypto.randomUUID() method is restricted to Secure Contexts (HTTPS or localhost). When running the app in a development environment or self-hosted setup accessed via a local IP address, the browser disables this API, resulting in the following error:

Uncaught TypeError: crypto.randomUUID is not a function
    at createOptimisticMessage (chat-screen-utils.ts:14:27)
    ...

The Fix

I added a randomUUID helper function in src/lib/utils.ts that:

1. Checks if window.crypto.randomUUID is available.
2. Falls back to a math-based UUID v4 generator if running in an insecure context.
   I then replaced all direct usages of crypto.randomUUID() with this new helper in:

• apps/webclaw/src/screens/chat/chat-screen.tsx
• apps/webclaw/src/screens/chat/chat-screen-utils.ts
• apps/webclaw/src/components/attachment-button.tsx

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How to Test

1. Start the dev server (pnpm dev).
2. Access the application using your machine's local LAN IP (e.g., http://192.168.x.x:3000) instead of localhost.
3. Try to make a new session or chat with an existing session.
   Before fix:

• The frontend page cannot make a new session or chat with old sessions.
• The console logs the error: crypto.randomUUID is not a function.
  After fix:
• New sessions function correctly.
• Chatting within existing sessions works as expected.

[ibelick]

could we switch the fallback to use crypto.getRandomValues instead of Math.random?