Add ConfigValidators and CreateDefaults hooks to the generic resource

Two things ResourceSpec could not express: plan-time checks that span
several attributes, and create bodies that need a key Dokploy insists on
receiving but the model cannot produce. Both are used by the commits that
follow.

internal/provider/generic.go

@@ -67,6 +67,16 @@ type ResourceSpec struct {
 	// discover the new ID.
 	ListIDs func(ctx context.Context, api *client.Client, model any) (map[string]struct{}, error)
 
+	// CreateDefaults supplies values for API fields that Dokploy's create
+	// schema insists on receiving but that the model cannot produce -- most
+	// often a name the server declines to generate. Only keys missing from
+	// the assembled body are added, so an explicit configuration always wins.
+	CreateDefaults func(model any) map[string]any
+
+	// ConfigValidators are plan-time checks that span several attributes, for
+	// invariants Terraform's schema cannot express on its own.
+	ConfigValidators []resource.ConfigValidator
+
 	// PostRead derives extra model fields from the raw read response, for
 	// values that are not plain top-level columns (for example a project's
 	// default environment, which arrives nested under `environments`).
@@ -83,6 +93,7 @@ var (
 	_ resource.Resource                     = &genericResource{}
 	_ resource.ResourceWithConfigure        = &genericResource{}
 	_ resource.ResourceWithImportState      = &genericResource{}
+	_ resource.ResourceWithConfigValidators = &genericResource{}
 )
 
 func newGenericResource(spec ResourceSpec) func() resource.Resource {
@@ -97,6 +108,10 @@ func (r *genericResource) Schema(_ context.Context, _ resource.SchemaRequest, re
 	resp.Schema = r.spec.Schema
 }
 
+func (r *genericResource) ConfigValidators(_ context.Context) []resource.ConfigValidator {
+	return r.spec.ConfigValidators
+}
+
 func (r *genericResource) Configure(_ context.Context, req resource.ConfigureRequest, resp *resource.ConfigureResponse) {
 	if req.ProviderData == nil {
 		return
@@ -125,6 +140,14 @@ func (r *genericResource) Create(ctx context.Context, req resource.CreateRequest
 		return
 	}
 
+	if r.spec.CreateDefaults != nil {
+		for key, value := range r.spec.CreateDefaults(model) {
+			if _, present := body[key]; !present {
+				body[key] = value
+			}
+		}
+	}
+
 	if r.spec.NeedsOrganizationID {
 		orgID, err := r.api.OrganizationID(ctx)
 		if err != nil {