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/Shared/Layout/NavMenu.razor

@@ -1,4 +1,5 @@
 @using WebApp.Models
+@using WebApp.Authentication
 @inject IConfiguration Configuration
 
 <MudPaper Width="250px" Class="d-inline-flex py-3" Elevation="0">
@@ -20,5 +21,10 @@
             <MudNavLink Href="/students/event-ranking" Icon="@AppIcons.EventRank">Event Ranking</MudNavLink>
             <MudNavLink Href="/teams/assignment" Icon="@AppIcons.TeamAssignment">Team Assignment</MudNavLink>
         </MudNavGroup>
+        <AuthorizeView Roles="Administrator">
+            <MudDivider Class="my-2"/>
+            <MudNavLink Href="/settings/chapter" Icon="@Icons.Material.Filled.School">Chapter Settings</MudNavLink>
+            <MudNavLink Href="/settings/validation" Icon="@Icons.Material.Filled.Settings">Validation Settings</MudNavLink>
+        </AuthorizeView>
     </MudNavMenu>
 </MudPaper>