fix: preserve DCR client info on disconnect to avoid re-registration errors

[peschee]

Summary

• Bug: On disconnect/reconnect, the Inspector clears all OAuth session state including the dynamically registered client information (client_id, client_secret). However, the DCR-obtained client_id remains valid at the IDP, so discarding it forces an unnecessary re-registration that IDPs like Keycloak reject with a conflict error.
• Root cause: clear() in auth.ts was wiping clientInformation from sessionStorage along with tokens and code verifier.
• Fix: Stop clearing dynamically registered client information in clear(). Only tokens and transient OAuth state are cleared, preserving the still-valid DCR client credentials for reconnection.

Test plan

• npm run build-client passes
• cd client && npm run lint passes
• Manual test: disconnect and reconnect to a Keycloak server — should reuse the existing DCR client without re-registration errors