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/Students/Registration.razor

@@ -2,8 +2,10 @@
 @attribute [Authorize]
 @using Microsoft.EntityFrameworkCore
 @using WebApp.Models
+@using Core.Validation
 @inject AppDbContext Context
 @inject WebApp.LocalStorageService LocalStorage
+@inject ValidationService ValidationService
 
 <PageTitle>Registration - TSA Chapter Organizer</PageTitle>
 
@@ -43,6 +45,11 @@
                 </MudTooltip>
             </CellTemplate>
         </PropertyColumn>
+        <TemplateColumn Title="Warnings" Sortable="false">
+            <CellTemplate>
+                <ValidationWarnings Warnings="@GetRegistrationWarnings(context.Item.Student)" />
+            </CellTemplate>
+        </TemplateColumn>
         @if (_showGrade)
         {
             <PropertyColumn Property="@(e => e.Student.Grade)" Title="Grade" Sortable="true" />
@@ -239,6 +246,20 @@
             : data.OrderBy(sortExpression);
     }
 
+    private List<ValidationWarning> GetRegistrationWarnings(Student student)
+    {
+        // Create StudentEventStatistics from the student's teams
+        var stats = new StudentEventStatistics
+        {
+            Student = student,
+            Events = student.Teams?.Where(t => t?.Event != null)
+                                  .Select(t => t.Event)
+                                  .ToList() ?? new List<EventDefinition>()
+        };
+
+        return ValidationService.ValidateStudentStatistics(stats, ValidationContext.StudentRegistration);
+    }
+
     public class StudentTeamInfo
     {
         public required Student Student { get; init; }