Potential fix for code scanning alert no. 4: Insecure randomness

[marceloceccon]

Potential fix for https://github.com/entropyvortex/clashcode/security/code-scanning/4

Use Node.js cryptographic randomness for key-like token generation in examples/keychain-setup.ts.

Best fix (without changing functionality):

• Import Node’s built-in crypto module (randomBytes).
• Replace the Math.random().toString(36).slice(2, 10) suffix with an 8-character suffix derived from randomBytes, e.g. randomBytes(6).toString('base64url').slice(0, 8).
  This preserves the same shape/purpose (short random demo suffix) while making randomness cryptographically secure.

Change only:

• examples/keychain-setup.ts:
  • Add import { randomBytes } from 'node:crypto'
  • Replace fake key generation line.

No changes are required in src/config/keychain.ts.

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