fix(examples): ADR-0079 — app-todo task uses nameField, not retired titleFormat

The app-todo example modeled the retired `titleFormat` pattern. With
autoprov (provisionPrimary at registry) now designating a derived
nameField, a render-only titleFormat is at best advisory and at worst
shadowed. Migrate to the canonical `nameField: 'subject'` so the example
demonstrates ADR-0079 best practice and the record-title gate stays
clean. Drops the now-unused `tmpl` import.

Author: os-zhuang

examples/app-todo/src/objects/task.object.ts

@@ -1,4 +1,4 @@
-import { P, tmpl } from '@objectstack/spec';
+import { P } from '@objectstack/spec';
 // Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
 
 import { ObjectSchema, Field } from '@objectstack/spec/data';
@@ -180,7 +180,7 @@ export const Task = ObjectSchema.create({
     { fields: ['category'] },
   ],
 
-  titleFormat: tmpl`{{record.subject}}`,
+  nameField: 'subject',
   compactLayout: ['subject', 'status', 'priority', 'due_date', 'owner'],
 
   validations: [