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/Pages/Contact.cshtml

@@ -38,7 +38,7 @@
 
     <form method="post" id="contactForm">
         @Html.AntiForgeryToken()
-        <div asp-validation-summary="ModelOnly" class="text-danger mb-3"></div>
+        <div asp-validation-summary="All" class="text-danger mb-3"></div>
 
         <div class="mb-3">
             <label for="name" class="form-label">이름 <span class="text-danger">*</span></label>
@@ -73,7 +73,7 @@
         </div>
 
         <div class="mb-3 form-check">
-            <input type="checkbox" class="form-check-input" id="agree" name="Agree" required />
+            <input type="checkbox" class="form-check-input" id="agree" name="Agree" value="true" required />
             <label class="form-check-label" for="agree">
                 개인정보 수집·이용에 동의합니다
             </label>