Add success-path tests for all template write endpoints

- POST /v3/templates (202): create template, validate schema, clean up
- POST /v2/templates (202): create template, validate schema, clean up
- PATCH /v2/templates/{templateID} (200): update public field, validate schema
- PATCH /templates/{templateID} (200): deprecated endpoint success test
- POST /v2/.../builds/{buildID} (202): start build on created template
- POST /templates/tags (201): assign tag using existing name:tag target
- DELETE /templates/tags (204): remove test tag
- DELETE /templates/{templateID}: real cleanup of test templates
- GET /templates/{templateID}/tags: discover existing tags in phase 2
- Drop minor findings from report and exit code (CI-oriented)

Author: beran-t