As a content creator, I want the option to load a sample template into the YAML editor with a single click.

Currently, the YAML editor in "Creator" mode is blank by default. To improve usability and guide new users, this ticket involves adding a button or link (e.g., "Load Sample Template") that, when clicked, populates the editor with a valid quickstart YAML structure. This provides an optional starting point without forcing a template on experienced users who may prefer to paste their own code into a blank editor.

Acceptance Criteria:

• When the user switches to "Preview" mode, the YAML editor is blank by default.
• A clearly visible button or link with text like "Load Sample Template" is present near the editor.
• Clicking this button populates the editor with the default, valid quickstart YAML template.
• The newly loaded template renders correctly in the Live card preview.