Fix runtime schema interfaces: restore isNode to NodeSpec, keep removed from FieldSpec

- Add isNode field back to NodeSpec interface while keeping it removed from FieldSpec
- Update runtime schema generator to include isNode in NodeSpec objects
- Update TypeScript generation to reflect correct interface structure
- Regenerate all runtime schema files and test snapshots
- Maintain enhanced AST generation functionality with corrected schema

Co-Authored-By: Dan Lynch <[email protected]>

Author: devin-ai-integration[bot]

__fixtures__/output/runtime-schema/full-features/complete-schema.json

@@ -53,6 +53,7 @@ export class RuntimeSchemaGenerator {
 
     return {
       name: type.name,
+      isNode: this.nodeTypes.has(type.name),
       fields: fields.sort((a, b) => a.name.localeCompare(b.name))
     };
   }

__fixtures__/output/runtime-schema/json/custom-filename/custom-node-specs.json

@@ -7,6 +7,7 @@ export interface FieldSpec {
 
 export interface NodeSpec {
   name: string;
+  isNode: boolean;
   fields: FieldSpec[];
 }