feat: email as mailto link + chat response rules tests (21 assertions)

- Email txeo.msx@gmail.com rendered as clickable mailto: link in chat
- New test: 86-chat-response-rules.test.mjs covering:
  contact (email shown, no contact form), phone (private),
  location (Lanzarote), language matching (EN/ES),
  off-topic redirect, tech search, no hallucination, years
- Tests are non-deterministic (live LLM) — may need re-runs

internal/chat/handler.go

@@ -319,6 +319,10 @@ func (h *Handler) formatResponse(text string) string {
 		text = strings.Replace(text, "**", "</strong>", 1)
 	}
 
+	// Email addresses → clickable mailto links
+	text = strings.ReplaceAll(text, "txeo.msx@gmail.com",
+		`<a href="mailto:txeo.msx@gmail.com" class="chat-nav-link">txeo.msx@gmail.com</a>`)
+
 	// Links: [text](#anchor) → icon + nav link, [text](https://...) → external link
 	text = mdLinkRe.ReplaceAllStringFunc(text, func(match string) string {
 		parts := mdLinkRe.FindStringSubmatch(match)