Migrate all interactive Blazor components to vanilla JS for full SSR

- Replace server interactivity with vanilla JS (forms.js) for Popover, Calendar, TimePicker, NumberInput, and Counter components

- Rewrite all Razor components to static SSR using data-* attributes for JS hooks

- Simplify InputBase.cs (remove EventCallback, EditContext, SetValueAsync)

- Remove AddInteractiveServerComponents/AddInteractiveServerRenderMode from Program.cs

- Update demo pages: remove @rendermode, replace EditForm with native form

- Add InteractivityGapTests.cs with 30 scoped E2E tests

- Update FormsTests.cs selectors for new static SSR structure

- Fix year picker navigation bug and date format mismatch in forms.js

- All 126 tests passing

Enciphered.Blazor.UIComponents.Demo/Program.cs

@@ -3,8 +3,7 @@ using Enciphered.Blazor.UIComponents.Demo.Components;
 var builder = WebApplication.CreateBuilder(args);
 
 // Add services to the container.
-builder.Services.AddRazorComponents()
-    .AddInteractiveServerComponents();
+builder.Services.AddRazorComponents();
 
 var app = builder.Build();
 
@@ -23,7 +22,6 @@ app.UseAntiforgery();
 
 app.MapStaticAssets();
 app.MapRazorComponents<App>()
-    .AddInteractiveServerRenderMode()
     .AddAdditionalAssemblies(typeof(Enciphered.Blazor.UIComponents.SidebarProvider).Assembly);
 
 app.Run();