feat: add random template button to playground

- Create 10 boilerplate templates (cards, nav, forms, animations, etc.)
- Add dice button (🎲) visible only in playground mode
- Load random template and apply to preview on click
- Templates include: Card, Navigation, Profile, Buttons, Pricing,
  Form, Features Grid, Badges, CSS Animation, Flexbox Layout

🤖 Generated with [Claude Code](https://claude.com/claude-code)

src/index.html

@@ -177,6 +177,9 @@
 										>
 											⟲
 										</button>
+										<button id="random-template-btn" class="btn btn-icon hidden" title="Load random template">
+											🎲
+										</button>
 									</div>
 									<button id="run-btn" class="btn btn-run"><img src="./gear.svg" alt="" /><span data-i18n="run">Run</span></button>
 								</div>