test(openbuilt-templates-marketplace): PHPUnit unit tests for seed + clone

Add two PHPUnit unit test suites (10 scenarios total):
- SeedApplicationTemplatesTest covers fresh-install seeding,
  idempotent re-run, slug-list verification, and loud-fail when
  an expected fixture file is missing (REQ-OBTC-002 / REQ-OBTC-009).
- CreateFromTemplateTest covers all six required branches for
  ApplicationsController::createFromTemplate: 404 unknown template,
  same-owner slug collision, success path with per-app register +
  prefixed companion schemas, manifest schema-ref rewrite walker,
  owner-field tagging from the authenticated session, and cross-user
  slug reuse (REQ-OBTC-004 / REQ-OBTC-005).

Author: rubenvdlinde