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

Core/Validation/Rules/BaseRules/EventCountThresholdRankingRuleBase.cs

@@ -0,0 +1,88 @@
+using Core.Entities;
+
+namespace Core.Validation.Rules.BaseRules;
+
+/// <summary>
+/// Base class for validation rules that check event counts against thresholds for student rankings
+/// Similar to EventCountThresholdRuleBase but works with Student entities instead of StudentEventStatistics
+/// </summary>
+public abstract class EventCountThresholdRankingRuleBase : IValidationRule<Student>
+{
+    /// <summary>
+    /// Get the actual count to validate
+    /// </summary>
+    protected abstract int GetCount(Student student);
+
+    /// <summary>
+    /// Get the threshold value from configuration
+    /// </summary>
+    protected abstract int GetThreshold(ValidationConfiguration config);
+
+    /// <summary>
+    /// Check if the count violates the threshold
+    /// </summary>
+    protected abstract bool ViolatesThreshold(int count, int threshold);
+
+    /// <summary>
+    /// Get the severity from configuration
+    /// </summary>
+    protected abstract ValidationSeverity GetSeverity(ValidationConfiguration config);
+
+    /// <summary>
+    /// The validation warning code
+    /// </summary>
+    protected abstract string Code { get; }
+
+    /// <summary>
+    /// Build the display message
+    /// </summary>
+    protected abstract string GetMessage(int count, int threshold);
+
+    /// <summary>
+    /// Icon identifier for the warning (can be null)
+    /// </summary>
+    protected virtual string? IconIdentifier => null;
+
+    /// <summary>
+    /// Build additional metadata beyond the standard fields
+    /// </summary>
+    protected virtual Dictionary<string, object> BuildAdditionalMetadata(Student student, ValidationConfiguration config)
+    {
+        return new Dictionary<string, object>();
+    }
+
+    public ValidationWarning? Validate(Student entity, ValidationConfiguration config)
+    {
+        var count = GetCount(entity);
+        var threshold = GetThreshold(config);
+
+        if (!ViolatesThreshold(count, threshold))
+            return null;
+
+        var metadata = new Dictionary<string, object>
+        {
+            { "StudentId", entity.Id },
+            { "StudentName", entity.FirstNameLastName }
+        };
+
+        // Add any additional metadata from derived class
+        foreach (var kvp in BuildAdditionalMetadata(entity, config))
+        {
+            metadata[kvp.Key] = kvp.Value;
+        }
+
+        return new ValidationWarning
+        {
+            Code = Code,
+            Message = GetMessage(count, threshold),
+            Severity = GetSeverity(config),
+            Context = ValidationContext.StudentRanking,
+            IconIdentifier = IconIdentifier,
+            Metadata = metadata
+        };
+    }
+
+    public bool AppliesTo(ValidationContext context) =>
+        context == ValidationContext.StudentRanking ||
+        context == ValidationContext.StudentRegistration;
+}