Use reflection to discover cascading parameters in ComponentRenderer

[Copilot]

Addresses feedback on #74 to remove hardcoded cascading parameter names that create tight coupling between ComponentRenderer and theme view base classes.

Changes

• Replace hardcoded HashSet of parameter names with reflection-based discovery
• Scan ScissorHands.Theme assembly at startup to detect properties with [CascadingParameter] attribute
• Use lazy initialization to minimize reflection overhead to one-time cost
• Add error handling for ReflectionTypeLoadException and use GetExportedTypes() for safety

Before

var cascadingKeys = new HashSet<string>(StringComparer.Ordinal)
{
    "Documents",
    "Document", 
    "Plugins",
    "Theme",
    "Site"
};

After

private static readonly Lazy<HashSet<string>> _cascadingParameterNames = new(() =>
{
    var parameterNames = new HashSet<string>(StringComparer.Ordinal);
    var themeAssembly = typeof(PageViewBase).Assembly;
    
    var allTypes = themeAssembly.GetExportedTypes();
    foreach (var type in allTypes)
    {
        var cascadingProperties = type.GetProperties(BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly)
            .Where(p => p.GetCustomAttribute<CascadingParameterAttribute>() is not null);
        
        foreach (var property in cascadingProperties)
            parameterNames.Add(property.Name);
    }
    
    return parameterNames;
});

New cascading parameters added to theme view base classes will be automatically discovered without requiring manual updates to the renderer.

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