refactor: simplify contact form timestamp with hyperscript + minimal JS

Replace 34-line IIFE/MutationObserver with:
- Hyperscript: on toggle if me.open call resetContactForm()
- 11-line resetContactForm() function

Also dispatches 'show' event from openModal() for ninja-keys integration.
All 7 contact form tests pass.

static/js/ninja-keys-init.js

@@ -48,6 +48,8 @@
       const modal = document.getElementById(modalId);
       if (modal && modal.showModal) {
         modal.showModal();
+        // Dispatch 'show' event for hyperscript handlers
+        modal.dispatchEvent(new CustomEvent('show'));
       }
       ninjaKeys.close();
     }