Release v20.51.0

Added

• Analyzer (ARC0010) that flags a [Command] Handle() returning Task/Task<T> without awaiting anything — including the Task.FromResult/Task.CompletedTask wrapper shape the compiler's own CS1998 does not catch — with a code fix that unwraps it to the synchronous return shape the command pipeline already accepts.
• Analyzer (ARC0011) that flags a [Roles(...)] string-literal argument, with a code fix that rewrites it to nameof(<EnumType>.<Member>) so a role rename becomes a compile error instead of a silent authorization failure.
• Analyzer (ARC0012) that flags built-in exception types (Exception, InvalidOperationException, ArgumentException, and the like) thrown from Arc artifacts — command Handle() methods, CommandValidator<T>/ConceptValidator<T> validators, and reactor handlers — steering domain failures toward domain-named exception types.