feat(coding): add durable project identity core

tests/unit/coding-projects-migration.test.ts

@@ -177,6 +177,7 @@ describe('coding project v1 to v2 migration', () => {
 
     expect(result.status).toBe('migrated');
     if (result.status !== 'migrated') throw new Error('Expected migrated result');
+    expect(result.config).not.toHaveProperty('projectId');
     expect(result.config.agents).toEqual([
       expect.objectContaining({
         id: 'unique',