feat(dashboard): add lock button to prevent accidental widget movement

- Add lock/unlock button to dashboard header (always visible)
- Lock state prevents dragging in both normal and edit modes
- Lock state prevents resizing in edit mode
- Icon changes: lock-open (unlocked) ↔ lock (locked)
- Hide resize handles and prevent grab cursor when locked
- Lock state persists across edit mode toggles
- Integrate lock checks in DragDropHandler and ResizeHandler
- Pass editManager reference to drag/resize handlers for lock state access

src/systems/dashboard/resizeHandler.js

@@ -27,6 +27,7 @@ export class ResizeHandler {
      */
     constructor(gridEngine, options = {}) {
         this.gridEngine = gridEngine;
+        this.editManager = options.editManager || null; // Reference to EditModeManager for lock state
         this.options = {
             showDimensions: true,
             showGrid: true,
@@ -92,12 +93,20 @@ export class ResizeHandler {
 
             const mouseDownHandler = (e) => {
                 if (e.button !== 0) return;
+                // Don't resize if widgets are locked
+                if (this.editManager?.isWidgetsLocked()) {
+                    return;
+                }
                 e.preventDefault();
                 e.stopPropagation();
                 this.startResize(e, handleType, element, widget, onResizeEnd, widgetConstraints);
             };
 
             const touchStartHandler = (e) => {
+                // Don't resize if widgets are locked
+                if (this.editManager?.isWidgetsLocked()) {
+                    return;
+                }
                 this.touchTimer = setTimeout(() => {
                     e.preventDefault();
                     e.stopPropagation();