loader.ts — resolve Ajv default export so tsc + ESM interop both work

Plain `import Ajv from 'ajv'` works at runtime (Node ESM, Vite) but tsc with
NodeNext sees Ajv as a namespace, not a constructor. Use namespace import +
runtime resolution of `.default ?? namespace` to satisfy both.

Author: perki

ts/appTemplates/loader.ts

@@ -15,13 +15,18 @@
  *   const tpl = await loadTemplateFromUrl(url);  // fetches then validates
  */
 
-import Ajv, { type ErrorObject, type ValidateFunction } from 'ajv';
+import * as AjvNs from 'ajv';
+import type { ErrorObject, ValidateFunction } from 'ajv';
+
+// Ajv ships an ESM default + CJS interop. `default` may be the class itself
+// or the namespace depending on bundler. Resolve once at load.
+const Ajv: any = (AjvNs as any).default ?? AjvNs;
 import { HDSLibError } from '../errors.ts';
 import schema from './schemas/appTemplate.schema.json' with { type: 'json' };
 import type { AppTemplate, CustomFieldDeclaration, ExistingStreamRef } from './templateTypes.ts';
 
 const ajv = new Ajv({ allErrors: true, strict: false });
-const validate: ValidateFunction<AppTemplate> = ajv.compile<AppTemplate>(schema as any);
+const validate: ValidateFunction<AppTemplate> = ajv.compile(schema as any);
 
 /** Validate the JSON shape (Ajv) and run cross-field rules. Returns the validated AppTemplate or throws HDSLibError. */
 export function loadTemplate (json: unknown): AppTemplate {