Add dashboard tab with real-time target status overview

Dashboard is the new default tab showing running/stopped targets
with FPS, uptime, errors metrics. Updates live via events WebSocket.
Includes Stop All button and Start/Stop per target.

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

server/src/wled_controller/static/index.html

@@ -35,10 +35,17 @@
 
         <div class="tabs">
             <div class="tab-bar">
+                <button class="tab-btn" data-tab="dashboard" onclick="switchTab('dashboard')"><span data-i18n="dashboard.title">📊 Dashboard</span></button>
                 <button class="tab-btn" data-tab="targets" onclick="switchTab('targets')"><span data-i18n="targets.title">⚡ Targets</span></button>
                 <button class="tab-btn" data-tab="streams" onclick="switchTab('streams')"><span data-i18n="streams.title">📺 Sources</span></button>
             </div>
 
+            <div class="tab-panel" id="tab-dashboard">
+                <div id="dashboard-content">
+                    <div class="loading-spinner"></div>
+                </div>
+            </div>
+
             <div class="tab-panel" id="tab-targets">
                 <div id="targets-panel-content">
                     <div class="loading-spinner"></div>
@@ -56,7 +63,7 @@
                 (function() {
                     var saved = localStorage.getItem('activeTab');
                     if (saved === 'devices') saved = 'targets';
-                    if (!saved || !document.getElementById('tab-' + saved)) saved = 'targets';
+                    if (!saved || !document.getElementById('tab-' + saved)) saved = 'dashboard';
                     document.querySelectorAll('.tab-btn').forEach(function(btn) { btn.classList.toggle('active', btn.dataset.tab === saved); });
                     document.querySelectorAll('.tab-panel').forEach(function(panel) { panel.classList.toggle('active', panel.id === 'tab-' + saved); });
                 })();