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/Components/App.razor

@@ -29,8 +29,10 @@
     <script type="module">
         import { init as initDarkMode } from '/_content/Enciphered.Blazor.UIComponents/js/darkmode.js';
         import { init as initSidebar } from '/_content/Enciphered.Blazor.UIComponents/js/sidebar.js';
+        import { init as initForms } from '/_content/Enciphered.Blazor.UIComponents/js/forms.js';
         initDarkMode();
         initSidebar();
+        initForms();
     </script>
 </body>