fix(api,admin-ui,user-ui): improve branding preview and jwks key handling

[markwylde]

Summary

• remove redundant back and refresh actions across admin create/edit/list pages to streamline navigation and reduce duplicate controls
• rework branding preview flow to support live theme + branding messages, mode-specific colors/assets, and safer default logo/favicon handling in admin preview and user-facing screens
• align JWKS handling in admin UI with API responses by deriving active keys from rotatedAt, normalizing key metadata, and exporting public JWKs from the keys table

Why

• simplified page actions keep navigation consistent with primary table/form actions
• branding preview should reflect light/dark edits immediately without reloads and without stale local theme state
• JWKS displays should track current key state accurately and support direct key export workflows

Validation

• npm run tidy
• npm run build