feat: Add plain text CV endpoint and contact form with security

Plain text endpoint:
- Add /text route for plain text CV (for curl/AI crawlers)
- Use k3a/html2text library for HTML-to-text conversion
- Add Plain Text button to hamburger menu with UI translations

Contact form feature:
- Add ContactHandler with proper email service integration
- Add CSRF protection middleware
- Add rate limiting (5 submissions/hour per IP)
- Add honeypot and timing-based bot protection
- Add input validation with detailed error messages
- Add security logging middleware
- Add browser-only middleware for API protection

Code quality:
- Fix all golangci-lint errcheck warnings for w.Write calls
- Remove duplicate getClientIP functions
- Wire up ContactHandler in routes.Setup

templates/partials/widgets/contact-button.html

@@ -0,0 +1,11 @@
+{{define "contact-button"}}
+<!-- Contact Button (Fixed Left) -->
+<button
+    id="contact-button"
+    class="fixed-btn contact-btn no-print has-tooltip"
+    onclick="document.getElementById('contact-modal').showModal()"
+    aria-label="{{.UI.Widgets.Contact.AriaLabel}}"
+    data-tooltip="{{.UI.Widgets.Contact.Tooltip}}">
+    <iconify-icon icon="mdi:email-outline" width="28" height="28"></iconify-icon>
+</button>
+{{end}}