Do not allow team assignment when other teams exist already

WebApp/Components/Features/Teams/Assignment.razor

@@ -297,8 +297,17 @@
     </MudItem>
 </MudGrid>
 
-<MudTooltip Text="This will overwrite existing teams">
-<MudButton Class="ma-3" StartIcon="@Icons.Material.Filled.Warning" Variant="Variant.Filled" Size="Size.Large" OnClick="SaveTeams" Color="Color.Warning">Save</MudButton>
+@if (_hasExistingTeams)
+{
+    <MudAlert Severity="Severity.Warning" Class="ma-3" Variant="Variant.Filled">
+        <strong>Cannot save:</strong> There are existing teams. Please delete all teams before saving a new assignment.
+        <MudButton Href="/teams" Variant="Variant.Text" Color="Color.Default" Class="ml-2">View Teams</MudButton>
+    </MudAlert>
+}
+
+<MudTooltip Text="@(_hasExistingTeams ? "Delete existing teams first" : "This will save the team assignments")">
+    <MudButton Class="ma-3" StartIcon="@Icons.Material.Filled.Warning" Variant="Variant.Filled" Size="Size.Large"
+               OnClick="SaveTeams" Color="Color.Warning" Disabled="@_hasExistingTeams">Save</MudButton>
 </MudTooltip>
 @code {
     public bool TestSwitch { get; set; } = false;
@@ -323,6 +332,7 @@
     private string _solutionStatus = string.Empty;
 
     private bool _isSolving = false;
+    private bool _hasExistingTeams = false;
 
     protected override async Task OnInitializedAsync()
     {
@@ -337,6 +347,9 @@
                 .ThenInclude(e => e.EventDefinition)
                 .Where(e => e.EventRankings.Any())
                 .OrderBy(e => e.FirstName).ToListAsync();
+
+        // Check if there are existing teams
+        _hasExistingTeams = await Context.Teams.AnyAsync();
     }
 
     private async Task AddTeam()