fix(auth): trim userinfo stored in session cookies

[liujunlinginternet-glitch]

Summary

• Filter OAuth2 userinfo before it is stored in the browser session cookie.
• Retain standard OIDC display fields and the configured user ID field.
• Prevent nested provider claims from exceeding browser cookie limits.

Testing

• uv run pytest tests/auth/test_oauth2_auth.py
• uv run pre-commit run --files veadk/auth/middleware/oauth2_auth.py tests/auth/test_oauth2_auth.py