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/TeamRules/MissingCaptainRule.cs

@@ -0,0 +1,40 @@
+using Core.Entities;
+
+namespace Core.Validation.Rules.TeamRules;
+
+/// <summary>
+/// Validation rule that checks if a team-based event has an assigned captain
+/// </summary>
+public class MissingCaptainRule : IValidationRule<Team>
+{
+    public ValidationWarning? Validate(Team entity, ValidationConfiguration config)
+    {
+        if (!config.RequireTeamCaptain)
+            return null;
+
+        // Individual events don't need captains
+        if (entity.Event.EventFormat == EventFormat.Individual)
+            return null;
+
+        if (entity.Captain != null)
+            return null;
+
+        return new ValidationWarning
+        {
+            Code = "MISSING_CAPTAIN",
+            Message = "Team has no captain assigned",
+            Severity = config.MissingCaptainSeverity,
+            Context = ValidationContext.Team,
+            IconIdentifier = "Captain",
+            Metadata = new Dictionary<string, object>
+            {
+                { "TeamId", entity.Id },
+                { "EventName", entity.Event.Name },
+                { "TeamSize", entity.Students.Count }
+            }
+        };
+    }
+
+    public bool AppliesTo(ValidationContext context) =>
+        context == ValidationContext.Team;
+}

Core/Validation/Rules/TeamRules/TeamSizeTooLargeRule.cs

@@ -0,0 +1,42 @@
+using Core.Entities;
+
+namespace Core.Validation.Rules.TeamRules;
+
+/// <summary>
+/// Validation rule that checks if a team has more members than the maximum allowed
+/// </summary>
+public class TeamSizeTooLargeRule : IValidationRule<Team>
+{
+    public ValidationWarning? Validate(Team entity, ValidationConfiguration config)
+    {
+        // Individual events don't have team size requirements
+        if (entity.Event.EventFormat == EventFormat.Individual)
+            return null;
+
+        var actualSize = entity.Students.Count;
+        var maxSize = entity.Event.MaxTeamSize;
+
+        if (actualSize <= maxSize)
+            return null;
+
+        return new ValidationWarning
+        {
+            Code = "TEAM_SIZE_TOO_LARGE",
+            Message = $"Team has {actualSize} members (max: {maxSize})",
+            Severity = ValidationSeverity.Error, // Always error - hard constraint
+            Context = ValidationContext.Team,
+            IconIdentifier = null,
+            Metadata = new Dictionary<string, object>
+            {
+                { "TeamId", entity.Id },
+                { "EventName", entity.Event.Name },
+                { "ActualSize", actualSize },
+                { "MinSize", entity.Event.MinTeamSize },
+                { "MaxSize", maxSize }
+            }
+        };
+    }
+
+    public bool AppliesTo(ValidationContext context) =>
+        context == ValidationContext.Team;
+}

Core/Validation/Rules/TeamRules/TeamSizeTooSmallRule.cs

@@ -0,0 +1,42 @@
+using Core.Entities;
+
+namespace Core.Validation.Rules.TeamRules;
+
+/// <summary>
+/// Validation rule that checks if a team has fewer members than the minimum required
+/// </summary>
+public class TeamSizeTooSmallRule : IValidationRule<Team>
+{
+    public ValidationWarning? Validate(Team entity, ValidationConfiguration config)
+    {
+        // Individual events don't have team size requirements
+        if (entity.Event.EventFormat == EventFormat.Individual)
+            return null;
+
+        var actualSize = entity.Students.Count;
+        var minSize = entity.Event.MinTeamSize;
+
+        if (actualSize >= minSize)
+            return null;
+
+        return new ValidationWarning
+        {
+            Code = "TEAM_SIZE_TOO_SMALL",
+            Message = $"Team has {actualSize} members (min: {minSize})",
+            Severity = config.TeamSizeSeverity,
+            Context = ValidationContext.Team,
+            IconIdentifier = null,
+            Metadata = new Dictionary<string, object>
+            {
+                { "TeamId", entity.Id },
+                { "EventName", entity.Event.Name },
+                { "ActualSize", actualSize },
+                { "MinSize", minSize },
+                { "MaxSize", entity.Event.MaxTeamSize }
+            }
+        };
+    }
+
+    public bool AppliesTo(ValidationContext context) =>
+        context == ValidationContext.Team;
+}