Add loading states to MudDataGrid components

Implemented loading indicators and progress colors for all MudDataGrid instances across Events, Students, Teams, and Registration components to enhance user experience during data loading operations.

docs/plans/style-improvements.md

@@ -127,7 +127,7 @@ This document outlines recommended style improvements to enhance the visual desi
 
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-### 5. Add Loading States
+### 5. Add Loading States ✅ COMPLETED
 **Locations**: All MudDataGrid and async components
 
 **Issue**: No visual feedback during data loading operations.
@@ -331,7 +331,7 @@ Consider using MudChip components with rank colors for better visual distinction
 
 ### Phase 2: Visual Polish (Medium Impact, Medium Effort)
 4. ✅ Refine typography hierarchy usage
-5. Add loading states to all grids
+5. ✅ Add loading states to all grids
 6. ✅ Wrap pages in consistent container styling
 
 ### Phase 3: Enhancements (Nice to Have)