feat: add draggable zoom control with close button and menu toggle

- Add close button (X) to zoom control widget
- Make zoom control draggable anywhere on screen
- Persist dragged position in localStorage (cv-zoom-position)
- Add "Zoom" button to action bar to show control when hidden
- Persist visibility state in localStorage (cv-zoom-visible)
- Cursor changes to "move" to indicate draggability
- Interactive elements (slider, buttons) don't trigger drag
- Position stays within viewport bounds
- All features work on desktop only (zoom hidden on mobile)

static/css/main.css

@@ -3474,7 +3474,7 @@ html {
 
 .zoom-control {
     position: fixed;
-    bottom: 100px; /* Increased from 70px to clear footer */
+    bottom: 100px; /* Default position, can be dragged */
     left: 50%;
     transform: translateX(-50%);
     z-index: 900;
@@ -3490,6 +3490,34 @@ html {
     transition: all 0.3s ease;
     opacity: 0.7;
     font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
+    cursor: move; /* Indicate draggability */
+    user-select: none; /* Prevent text selection while dragging */
+}
+
+/* Close button for zoom control */
+.zoom-close-btn {
+    position: absolute;
+    top: -8px;
+    right: -8px;
+    width: 24px;
+    height: 24px;
+    background: rgba(220, 53, 69, 0.9);
+    border: 2px solid rgba(255, 255, 255, 0.3);
+    border-radius: 50%;
+    color: white;
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    padding: 0;
+    transition: all 0.2s ease;
+    z-index: 1;
+}
+
+.zoom-close-btn:hover {
+    background: rgba(220, 53, 69, 1);
+    transform: scale(1.1);
+    box-shadow: 0 2px 8px rgba(220, 53, 69, 0.4);
 }
 
 .zoom-control:hover {