Add optional client logo field to improve user identification on consent screen

[leodip]

Problem

Currently, the consent screen only displays the client identifier and description text. Users may have difficulty visually identifying
legitimate clients, especially when client identifiers are technical strings (e.g., my-app-prod-12345).

RFC 6749 Section 10.2 recommends that the authorization server "engage the resource owner to assist in identifying the client and its
origin."

Current Behavior

{{.clientIdentifier}}{{if .clientDescription}} - {{.clientDescription}}{{end}}

Proposed Solution

1. Add optional LogoURL field to the Client model (src/core/models/client.go)
2. Update admin console to allow logo upload/URL configuration
3. Display logo on consent screen when available
4. Consider adding optional WebsiteURL field for additional verification