feat: Add minimize button to Lightning stats panel

Added minimize/maximize functionality to Lightning Activity panel:
- Click header or toggle button (▼/▶) to minimize/maximize
- State persists in localStorage (lightning-stats-minimized)
- Minimized state restores on page reload
- Consistent with WSPR and Gray Line plugins

All control panels now have minimize functionality:
- WSPR: Filter, Stats, Legend, Chart panels ✓
- Gray Line: Control panel ✓
- Lightning: Stats panel ✓ (NEW)
- Earthquakes: No control panels (markers only)
- Aurora: No control panels (overlay only)
- Weather Radar: No control panels (tile layer only)

src/plugins/layers/useLightning.js

@@ -274,9 +274,11 @@ export function useLayer({ enabled = false, opacity = 0.9, map = null }) {
         
         div.innerHTML = `
           <div style="background: rgba(0, 0, 0, 0.8); color: white; padding: 10px; border-radius: 8px; font-family: 'JetBrains Mono', monospace; font-size: 11px; min-width: 180px;">
-            <div style="font-weight: bold; font-size: 14px; margin-bottom: 8px; display: flex; align-items: center; gap: 8px;">
+            <div style="font-weight: bold; font-size: 14px; margin-bottom: 8px; display: flex; align-items: center; justify-content: space-between; cursor: pointer;" class="lightning-stats-header">
               <span>⚡ Lightning Activity</span>
+              <span class="lightning-stats-toggle" style="font-size: 12px; cursor: pointer; user-select: none;">▼</span>
             </div>
+            <div class="lightning-stats-content">
               <table style="width: 100%; font-size: 11px;">
                 <tr><td>Fresh (&lt;1 min):</td><td style="text-align: right; color: #FFD700;">${fresh}</td></tr>
                 <tr><td>Recent (&lt;5 min):</td><td style="text-align: right; color: #FFA500;">${recent}</td></tr>
@@ -290,8 +292,27 @@ export function useLayer({ enabled = false, opacity = 0.9, map = null }) {
                 Updates every 30s
               </div>
             </div>
+          </div>
         `;
 
+        // Add minimize/maximize functionality
+        const header = div.querySelector('.lightning-stats-header');
+        const content = div.querySelector('.lightning-stats-content');
+        const toggle = div.querySelector('.lightning-stats-toggle');
+        
+        const minimized = localStorage.getItem('lightning-stats-minimized') === 'true';
+        if (minimized) {
+          content.style.display = 'none';
+          toggle.textContent = '▶';
+        }
+        
+        header.addEventListener('click', () => {
+          const isMinimized = content.style.display === 'none';
+          content.style.display = isMinimized ? 'block' : 'none';
+          toggle.textContent = isMinimized ? '▼' : '▶';
+          localStorage.setItem('lightning-stats-minimized', !isMinimized);
+        });
+
         // Prevent map interaction on control
         L.DomEvent.disableClickPropagation(div);
         L.DomEvent.disableScrollPropagation(div);