fix: per-page WASM render mode, Contact checkbox binding, Telegram inquiry channel

- Admin: replace the global @rendermode on <Routes>/<Router> with per-page
  render mode. Login.razor now prerenders (form visible before WASM loads);
  every other [Authorize] page stays prerender: false to avoid the
  AuthorizeRouteView blank-render regression from earlier attempts. Adds a
  "준비 중" -> "로그인" splash tied to WASM boot completion, and lets the
  authenticated-shell loading overlay stay up until AdminShell actually renders.
- Contact.cshtml: fix the "Agree" checkbox missing value="true" - a checked
  box sent the browser-default "on", which bool model binding can't parse,
  so ModelState.IsValid silently went false and OnPostAsync returned a blank
  form with no visible error on every submission. Validation summary widened
  from ModelOnly to All so this class of failure isn't silent again.
- TelegramInquiryNotificationService: read Telegram:InquiryChatId (falling
  back to ChatId) instead of only ChatId, matching the channel routing
  CLAUDE.md documents and deploy.yml already provisions as separate secrets.
- Reconcile CLAUDE.md's self-contradicting Phase 8 prerender notes (Phase 9),
  rewrite validate_admin_render.sh for the per-page design, and add a
  SmartAdmin 5.5 design reference section to DOUZONE_UX_GUIDE.md for future
  admin screens (existing screens unchanged, tracked as WBS P4-03).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

TaxBaik.Web/wwwroot/js/admin-session.js

@@ -239,11 +239,12 @@ window.taxbaikAdminSession = {
         window.addEventListener('hashchange', window.taxbaikAdminSession.syncRouteClass);
 
         if (document.documentElement.classList.contains('admin-login-route')) {
+            // Login prerenders immediately; no boot splash needed.
             window.taxbaikAdminSession.hideLoading();
         }
-
-        // Keep the initial overlay hidden unless explicitly enabled elsewhere.
-        window.taxbaikAdminSession.hideLoading();
+        // Non-login routes: leave the overlay showing until AdminShell's
+        // OnAfterRenderAsync(firstRender) calls hideLoading once WASM has
+        // actually rendered the authenticated shell.
 
         const modal = document.getElementById('components-reconnect-modal');
         if (!modal) return;
@@ -266,6 +267,16 @@ window.taxbaikAdminSession = {
 
         form.dataset.bound = '1';
         window.taxbaikAdminSession.traceUiState('admin-login', 'bindLoginForm attached');
+
+        // 업데이트 스플래시: 제출 핸들러가 실제로 붙기 전까지는 버튼을 "준비 중" 상태로 두고,
+        // 여기서 활성화해 사용자가 로그인 가능 시점을 알 수 있게 한다.
+        const readyButton = form.querySelector('#admin-login-submit');
+        if (readyButton) {
+            readyButton.disabled = false;
+            const label = readyButton.querySelector('span');
+            if (label) label.textContent = '로그인';
+        }
+
         form.addEventListener('submit', async function (event) {
             event.preventDefault();