Add comprehensive validation system with runtime configuration

Implements a flexible validation framework for student rankings, team assignments, and team composition with administrator-configurable rules and thresholds.

Validation System:
- Reflection-based rule discovery eliminates manual registration
- Base classes (RequiredEventTypeRuleBase, EventCountThresholdRuleBase) reduce code duplication by ~250 lines
- 12 validation rules covering event requirements, counts, and team constraints
- Configurable severity levels (Warning/Error) per rule type
- ValidationService with caching for optimal performance
- Rules apply contextually (StudentRanking, StudentAssignment, TeamComposition)

Configuration & Admin UI:
- ValidationSettings admin page for editing thresholds and severity levels
- ChapterSettings admin page for editing chapter information
- Settings stored in Data/appsettings.json for runtime configuration
- JSON config works in both development and production environments
- Auto-creates Data directory and config template on first run

User Experience:
- ValidationWarnings component displays inline warnings/errors
- Integrated in Event Ranking, Registration, and Team Assignment pages
- Color-coded severity indicators (warning yellow, error red)
- Includes "Too Many Regional Events" rule (max 3 recommended)

Technical Improvements:
- Template Method pattern for rule base classes
- Singleton rule instances with lazy initialization
- Configuration loaded via IConfiguration with fallback to defaults
- Safe JSON updates preserve other appsettings sections

WebApp/Components/Features/Teams/Assignment.razor

@@ -1,12 +1,14 @@
 @page "/teams/assignment"
 @attribute [Authorize]
 @using Core.Calculation
+@using Core.Validation
 @using Microsoft.EntityFrameworkCore
 @using WebApp.Models
 @using EventAssignment = Core.Calculation.EventAssignment
 @inject AppDbContext Context
 @inject IDialogService DialogService
 @inject NavigationManager NavigationManager
+@inject ValidationService ValidationService
 
 <PageTitle>Event Assignment - TSA Chapter Organizer</PageTitle>
 
@@ -134,18 +136,8 @@
                 <MudTd><b>@context.Student.FirstName</b></MudTd>
                 <MudTd>@context.EventCount</MudTd>
                 <MudTd>@context.TotalLevelOfEffort</MudTd>
-                <MudTd>@if (!context.HasOnSiteActivity)
-                       {
-                           <MudTooltip Text="No On-Site Activity">
-                            <MudText Style="font-weight:bolder" Color="Color.Warning">@AppIcons.OnSiteActivity</MudText>
-                           </MudTooltip>
-                       }
-                    @if (!context.HasRegionalEvent)
-                    {
-                        <MudTooltip Text="No Regional Event">
-                            <MudText Style="font-weight:bolder" Color="Color.Warning">@AppIcons.RegionalEvent</MudText>
-                        </MudTooltip>
-                    }
+                <MudTd>
+                    <ValidationWarnings Warnings="@GetStatisticsWarnings(context)" />
                 </MudTd>
             </RowTemplate>
             <ChildRowContent>
@@ -313,6 +305,7 @@
     public bool TestSwitch { get; set; } = false;
 
     private readonly AssignmentParameters _parameters = new() { RequireOnSite = false, RequireRegional = false };
+    private ValidationService _validationService = new ValidationService(ValidationConfiguration.Default);
 
     private List<EventDefinition>? _events;
     private List<Student>? _students;
@@ -367,6 +360,7 @@
     private async Task<TableData<Team>> SolveAssignments(TableState arg1, CancellationToken arg2)
     {
         _isSolving = true;
+        UpdateValidationConfig();
         var eventAssignment = new EventAssignment(_events, _students, _parameters);
         foreach (var requirement in _assignmentRequirements)
         {
@@ -396,6 +390,17 @@
         return new TableData<StudentEventStatistics> {Items = _statistics};
     }
 
+    private void UpdateValidationConfig()
+    {
+        var config = ValidationConfiguration.FromAssignmentParameters(_parameters);
+        _validationService = new ValidationService(config);
+    }
+
+    private List<ValidationWarning> GetStatisticsWarnings(StudentEventStatistics stats)
+    {
+        return _validationService.ValidateStudentStatistics(stats, ValidationContext.StudentAssignment);
+    }
+
     private async Task<TableData<AssignmentRequirement>> ReloadAssignmentRequirements(TableState arg1, CancellationToken arg2)
     {
         return new TableData<AssignmentRequirement> { Items = _assignmentRequirements };