Add interactive getting-started tutorial for first-time users

Auto-starts on first visit with a 9-step walkthrough covering header,
tabs, settings, search, theme, and language controls. Stores completion
in localStorage; restart via ? button in the header. Includes en/ru/zh
translations for all tour steps.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/templates/index.html

@@ -28,6 +28,9 @@
             </div>
             <div class="server-info">
                 <a href="/docs" target="_blank" class="header-link" data-i18n-title="app.api_docs" title="API Docs">API</a>
+                <button class="search-toggle" id="tour-restart-btn" onclick="startGettingStartedTutorial()" data-i18n-title="tour.restart" title="Restart tutorial">
+                    ?
+                </button>
                 <button class="search-toggle" onclick="openCommandPalette()" data-i18n-title="search.open" title="Search (Ctrl+K)">
                     🔍
                 </button>