Fix i18n for form placeholders and make snowflake emoji clickable

- Add data-i18n-placeholder support to i18n.js for dynamic placeholder translation
- Update form inputs with proper i18n attributes for placeholders and labels
- Make snowflake emoji (❄️) clickable on all pages to return to homepage
- Remove snowflake from translation strings since it's now a separate element
- Add i18n support to README features list

🤖 Generated with [Claude Code](https://claude.ai/code)

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

public/admin.html

@@ -57,7 +57,7 @@
         <!-- Admin Section -->
         <div id="admin-section" class="admin-section">
             <div class="admin-header">
-                <h1>❄️ Great Lakes Ice Report Admin Panel</h1>
+                <h1><a href="/" style="text-decoration: none; color: inherit;">❄️</a> Great Lakes Ice Report Admin Panel</h1>
                 <div class="header-buttons">
                     <button id="theme-toggle" class="header-btn theme-toggle-admin" title="Toggle dark mode">
                         <span class="theme-icon">🌙</span>