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)

templates/index.html

@@ -174,6 +174,15 @@
 
             <!-- Right: Action buttons -->
             <div class="action-buttons-right">
+                <button
+                    id="show-zoom-btn"
+                    class="action-btn zoom-toggle-btn"
+                    onclick="showZoomControl()"
+                    style="display: none;"
+                    aria-label="{{if eq .Lang "es"}}Mostrar control de zoom{{else}}Show zoom control{{end}}">
+                    <iconify-icon icon="mdi:magnify" width="18" height="18"></iconify-icon>
+                    {{if eq .Lang "es"}}Zoom{{else}}Zoom{{end}}
+                </button>
                 <button
                     class="action-btn pdf-btn"
                     onclick="openPdfModal()"
@@ -454,8 +463,16 @@
         </div>
     </div>
 
-    <!-- Zoom Control (Fixed Bottom Center) -->
+    <!-- Zoom Control (Fixed Bottom Center, Draggable) -->
     <div id="zoom-control" class="zoom-control no-print" role="group" aria-label="{{if eq .Lang "es"}}Control de zoom{{else}}Zoom control{{end}}">
+        <button
+            id="zoom-close"
+            class="zoom-close-btn"
+            aria-label="{{if eq .Lang "es"}}Cerrar control de zoom{{else}}Close zoom control{{end}}"
+            title="{{if eq .Lang "es"}}Cerrar{{else}}Close{{end}}">
+            <iconify-icon icon="mdi:close" width="16" height="16"></iconify-icon>
+        </button>
+
         <span class="zoom-value zoom-value-min" aria-hidden="true">50</span>
 
         <input