refactor(ui-common): derive ClientConfig and AuthenticationConfig from Zod schemas

refactor(ui-common): derive ClientConfig and AuthenticationConfig from Zod schemas

Replace two hand-written interfaces in client/types.ts with type aliases
derived from the Zod-inferred UIServerConfigurationSection:
- AuthenticationConfig = NonNullable<UIServerConfigurationSection['authentication']>
- ClientConfig = Omit<UIServerConfigurationSection, 'name'>

This eliminates duplication: protocol/version now carry enum types (Protocol,
ProtocolVersion) instead of loose strings. Update WebSocketClient.test.ts to
use Protocol.UI and ProtocolVersion['0.0.1'] enum values accordingly.