fix(dashboard): fix resize, drag-drop, overflow, and add auto-migration

Multiple critical fixes for dashboard v2:

**1. ResizeHandler error - updateContainerWidth is not a function**
- resizeHandler.js:288 was calling non-existent method
- Removed call - containerWidth tracked by ResizeObserver
- Resizing now functional

**2. DragDrop bug - widgets can't be released**
- endDrag() destructured widgets, originalX, originalY from dragState
- These fields were never added in startDrag()
- Added widgets parameter to initWidget() and startDrag()
- Store originalX, originalY, widgets in dragState
- dashboardManager now passes current tab widgets
- Widgets can now be dropped properly

**3. Widget content overflow**
- Added base .rpg-widget CSS: overflow: hidden, box-sizing: border-box
- Prevents content extending beyond widget bounds
- max-width: 100% on children

**4. Automatic layout migration**
- Old 12-column layouts (w: 8, w: 12) cause 500%+ widths in 2-4 column grid
- Added migrateOldLayouts() method
- Detects widgets with w > current column count
- Runs auto-layout to reposition for responsive grid
- Clears and re-renders current tab with new positions
- Saves migrated layout automatically

**5. Tab rendering**
- Implemented renderTabs() method
- Displays tab buttons with icons and names
- Active state highlighting
- Click handlers to switch tabs

**6. Collision prevention**
- Modified dragDrop endDrag() to check collisions
- Same-size widgets: swap positions
- Different sizes: revert to original
- Prevents overlapping widgets

**7. Edit mode fixes**
- Fixed edit button to call toggleEditMode()
- Added CSS to hide resize handles when not in edit mode
- Handles only visible in edit mode

**8. Icon-only header buttons**
- Auto-Arrange and Edit buttons now icon-only
- Saves horizontal space in header

All issues from user testing resolved.

src/systems/dashboard/dashboardIntegration.js

@@ -138,15 +138,12 @@ function getInlineDashboardTemplate() {
                 <div class="rpg-dashboard-header-right">
                     <button id="rpg-dashboard-auto-layout" class="rpg-dashboard-btn rpg-auto-layout-btn" title="Auto-Arrange Widgets">
                         <i class="fa-solid fa-table-cells-large"></i>
-                        <span>Auto-Arrange</span>
                     </button>
                     <button id="rpg-dashboard-edit-mode" class="rpg-dashboard-btn rpg-edit-mode-btn" title="Toggle Edit Mode">
                         <i class="fa-solid fa-pen-to-square"></i>
-                        <span>Edit</span>
                     </button>
                     <button id="rpg-dashboard-add-widget" class="rpg-dashboard-btn rpg-add-widget-btn" style="display: none;" title="Add Widget">
                         <i class="fa-solid fa-plus"></i>
-                        <span>Add Widget</span>
                     </button>
                     <button id="rpg-dashboard-export-layout" class="rpg-dashboard-btn rpg-export-btn" style="display: none;" title="Export Layout">
                         <i class="fa-solid fa-download"></i>
@@ -202,9 +199,9 @@ function setupDashboardEventListeners(dependencies) {
     const editModeBtn = document.querySelector('#rpg-dashboard-edit-mode');
     if (editModeBtn) {
         editModeBtn.addEventListener('click', () => {
-            if (dashboardManager) {
-                const isEditMode = dashboardManager.editModeManager.isEditMode();
-                dashboardManager.editModeManager.setEditMode(!isEditMode);
+            if (dashboardManager && dashboardManager.editManager) {
+                console.log('[RPG Companion] Edit button clicked');
+                dashboardManager.editManager.toggleEditMode();
             }
         });
     }