chore: drop the skills OAuth scopes the API no longer defines (#98)

nominal#2912 removed the skills API and cli#95 removed the skill commands;
the sign-in flow still asked for skills:delete/read/write. Nothing consumes
them, so the consent screen lists three scopes that do nothing.

Co-authored-by: Justin Helmer <justin@coreplane.ai>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

Author: 3 people

src/auth/oauth.ts

@@ -78,9 +78,6 @@ export const DEFAULT_SCOPES = [
   'repositories:delete',
   'repositories:read',
   'repositories:write',
-  'skills:delete',
-  'skills:read',
-  'skills:write',
   'subscriptions:read',
   'subscriptions:write',
   'teams:delete',