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.Client/Components/Admin/Pages/Clients/ClientDetail.razor

@@ -1,5 +1,5 @@
 @page "/admin/clients/{ClientId:int}"
-@rendermode InteractiveWebAssembly
+@rendermode @(new InteractiveWebAssemblyRenderMode(prerender: false))
 @attribute [Authorize]
 @using TaxBaik.Web.Services
 @using TaxBaik.Web.Services.AdminClients