A contact form that works on my host

Add a contact form to my site. Stack: <stack>. Host: <host>.

- Name, email and message. Validated in the browser for speed and on the
  server because that's the one that counts.
- Sending: through this host's mail, or a sending service? Pick the one
  that will actually arrive, and say why.
- Spam protection without a captcha: a hidden honeypot field and a time
  check.
- A clear success message on the same page, and a real error if sending
  fails, never a fake "thanks".
- The visitor's address goes in Reply-To, never in From, or the message
  will be treated as forged.

Show me every file that changes.