Introduce oauth2scope registry with freeze lifecycle

Replace pkg/iam/scopeset with pkg/iam/oauth2scope.Registry, a shared
OAuth2 scope→action registry used by the authorizer, OAuth2 service,
and Connect API. Registration stays open until probod calls Freeze();
read paths (RegisteredScopes, Allows, ValidateScopes) panic before
that.

Drop the leaky APIScopes surface and AllowedAPIScopes on manual
access-token creation in favor of registry.ValidateScopes. Metadata,
protected-resource metadata, and CIMD scope lists are built from
RegisteredScopes() via helpers in pkg/iam/oauth2/scopes.go. Expose
oauth2ScopesSupported as an OAuth2Scope GraphQL scalar.

Signed-off-by: Ludovic Vielle <ludovic@probo.com>

pkg/server/api/connect/v1/graphql_handler.go

@@ -37,6 +37,7 @@ func NewGraphQLHandler(svc *iam.Service, logger *log.Logger, fileManagerSvc *fil
 			batchAuthorize: authz.NewBatchAuthorizeFunc(svc, logger),
 			logger:         logger,
 			iam:            svc,
+			scopeRegistry:  svc.OAuth2ScopeRegistry,
 			fileManager:    fileManagerSvc,
 			baseURL:        baseURL,
 			sessionCookie:  authn.NewCookie(&cookieConfig),