🔒 Security fix: Enforce JWT audience verification

[eterna2]

🎯 What: Modified KestIdentityMiddleware to accept an audience parameter and removed the insecure verify_aud=False option when decoding JWTs via PyJWT.
⚠️ Risk: Without audience verification, JWTs issued for other clients or services could be used to authenticate requests, enabling potential token replay attacks across services.
🛡️ Solution: The middleware now safely passes the explicitly provided audience parameter down to PyJWT so it properly validates the token's aud claim. Added audience="account" to the configured middlewares in app.py, gateway.py, and agent.py to match the expected client tokens from Keycloak.

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PR created automatically by Jules for task 3046650064226689549 started by @eterna2

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