CLI error class semantics

Use ContextError for omitted required values, ResolutionError for supplied values not found, and fielded ValidationError for malformed input. Always rethrow AuthError so auto-login can trigger and HostScopeError so host-scoping rejection reaches the user; broad wrapping looks consistent but destroys these control-flow contracts. ContextError.command is one single-line usage example, with alternatives: [] when defaults are irrelevant.