feat(contact): implement Formspree contact form submission

- Enable contact form fields with component IDs
- Add callback for Formspree POST with JSON/AJAX
- Include honeypot spam protection (_gotcha field)
- Handle validation, loading, success/error states
- Clear form on successful submission
- Add lessons learned documentation

Closes #92, #93, #94

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

portfolio_app/callbacks/__init__.py

@@ -1,5 +1,5 @@
 """Application-level callbacks for the portfolio app."""
 
-from . import sidebar, theme
+from . import contact, sidebar, theme
 
-__all__ = ["sidebar", "theme"]
+__all__ = ["contact", "sidebar", "theme"]