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.

style.css

@@ -1073,12 +1073,56 @@ body:has(.rpg-panel.rpg-position-left) #sheld {
     flex-wrap: wrap;
 }
 
-.rpg-dashboard-btn {
+.rpg-dashboard-tabs {
+    display: flex;
+    align-items: center;
+    gap: 0.25rem;
+    flex-wrap: wrap;
+}
+
+.rpg-dashboard-tab {
     display: inline-flex;
     align-items: center;
     gap: 0.3rem;
-    padding: 0.4rem 0.6rem;
+    padding: 0.4rem 0.7rem;
     font-size: 0.75rem;
+    border: 1px solid transparent;
+    background: transparent;
+    color: var(--SmartThemeBodyColor);
+    border-radius: 6px;
+    cursor: pointer;
+    transition: all 0.2s;
+    opacity: 0.6;
+}
+
+.rpg-dashboard-tab:hover {
+    background: var(--SmartThemeBlurTintColor);
+    opacity: 0.9;
+}
+
+.rpg-dashboard-tab.active {
+    background: var(--SmartThemeBlurTintColor);
+    border-color: var(--SmartThemeBorderColor);
+    opacity: 1;
+    font-weight: 600;
+}
+
+.rpg-tab-icon {
+    font-size: 0.9rem;
+}
+
+.rpg-tab-name {
+    font-size: 0.75rem;
+}
+
+.rpg-dashboard-btn {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    padding: 0.5rem;
+    width: 2rem;
+    height: 2rem;
+    font-size: 0.9rem;
     border: 1px solid var(--SmartThemeBorderColor);
     background: var(--SmartThemeBlurTintColor);
     color: var(--SmartThemeBodyColor);
@@ -1093,7 +1137,7 @@ body:has(.rpg-panel.rpg-position-left) #sheld {
 }
 
 .rpg-dashboard-btn i {
-    font-size: 0.85rem;
+    font-size: 0.9rem;
 }
 
 .rpg-dashboard-grid {
@@ -1102,6 +1146,19 @@ body:has(.rpg-panel.rpg-position-left) #sheld {
     min-height: 200px;
 }
 
+/* Hide resize handles by default */
+.resize-handles {
+    opacity: 0;
+    pointer-events: none;
+    transition: opacity 0.2s;
+}
+
+/* Show resize handles in edit mode */
+.edit-mode .resize-handles {
+    opacity: 1;
+    pointer-events: auto;
+}
+
 /* ========================================
    DASHBOARD V2 WIDGET STYLES
    ========================================
@@ -1116,6 +1173,19 @@ body:has(.rpg-panel.rpg-position-left) #sheld {
    - %: Container-relative sizing
    ======================================== */
 
+/* Base widget container - ensures content stays within bounds */
+.rpg-widget {
+    box-sizing: border-box;
+    overflow: hidden;
+    display: flex;
+    flex-direction: column;
+}
+
+.rpg-widget > * {
+    box-sizing: border-box;
+    max-width: 100%;
+}
+
 .rpg-widget .rpg-stats-content {
     display: flex;
     flex-direction: column;  /* Stack vertically */