fix: prevent blank screen for new users migrating to widget dashboard

Fixed critical initialization timing bug where new users saw a blank screen
with error "Tab not found: main" when migrating from v1.x to v2.0.

Root Cause:
- dashboardManager.init() created a premature fallback "main" tab before
  loading the default layout
- TabManager was initialized with activeTabId='main'
- loadLayout() then replaced tabs with proper IDs ('tab-status', etc.)
- TabManager still referenced the non-existent 'main' tab
- Result: blank screen

Changes:
1. Removed premature fallback tab creation (lines 189-198)
   - Default layout is always set via setDefaultLayout() before init()
   - No need to create "main" tab before layout loads

2. Added safety check after loadLayout() completes (line 1506-1520)
   - If no tabs exist after loading, create emergency fallback
   - Uses correct tab ID 'tab-status' instead of 'main'
   - Updates TabManager's activeTab to match

Flow now:
- init() creates TabManager with empty tabs
- loadLayout() populates tabs from default or saved layout
- Safety check ensures at least one tab exists
- TabManager references only valid tab IDs

Fixes blank screen bug for users migrating from v1.x to v2.0.

src/systems/dashboard/dashboardManager.js

@@ -185,18 +185,8 @@ export class DashboardManager {
         });
 
         // Initialize Tab Manager with dashboard data structure
-        // Create default tab if no tabs exist
-        if (this.dashboard.tabs.length === 0) {
-            this.dashboard.tabs.push({
-                id: 'main',
-                name: 'Main',
-                icon: 'fa-solid fa-house',
-                order: 0,
-                widgets: []
-            });
-            this.dashboard.defaultTab = 'main';
-        }
-
+        // Note: Tabs will be populated by loadLayout() which runs after init()
+        // Default layout is set via setDefaultLayout() before init() is called
         this.tabManager = new TabManager(this.dashboard);
 
         // Set current tab to active tab from TabManager
@@ -1512,6 +1502,22 @@ export class DashboardManager {
                 this.applyDashboardConfig(this.defaultLayout);
             }
         }
+
+        // Safety check: If still no tabs after loading, create emergency fallback
+        // This should never happen if setDefaultLayout() was called properly
+        if (this.dashboard.tabs.length === 0) {
+            console.warn('[DashboardManager] No tabs loaded, creating emergency fallback');
+            this.dashboard.tabs.push({
+                id: 'tab-status',
+                name: 'Status',
+                icon: 'fa-solid fa-user',
+                order: 0,
+                widgets: []
+            });
+            this.dashboard.defaultTab = 'tab-status';
+            // Update TabManager's active tab
+            this.tabManager.setActiveTab('tab-status');
+        }
     }
 
     /**