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>

tests/e2e/contact-submit.spec.ts

@@ -54,4 +54,25 @@ test.describe('contact submit', () => {
     await navigateInBlazor(page, `${baseUrl}/admin/inquiries`);
     await expect(page.locator('.mud-main-content').getByText('문의 관리').first()).toBeVisible({ timeout: 20_000 });
   });
+
+  test('submitting the public Contact.cshtml form shows the success message', async ({ page }) => {
+    // Regression test: Contact.cshtml's "Agree" checkbox had no value="true", so a
+    // checked box submitted the browser-default "on", which bool model binding
+    // cannot parse. ModelState.IsValid became false and OnPostAsync silently
+    // returned Page() with a blank form and no visible error - the "무한 작성 유도"
+    // bug. This drives the real form through a browser to catch that class of bug.
+    const stamp = Date.now();
+
+    await page.goto(`${baseUrl}/contact`, { waitUntil: 'networkidle' });
+
+    await page.fill('#name', `Contact-E2E-${stamp}`);
+    await page.fill('#phone', '010-1234-5678');
+    await page.fill('#email', `contact-e2e-${stamp}@example.com`);
+    await page.fill('#message', 'Playwright로 Contact.cshtml 폼을 직접 제출한 테스트입니다.');
+    await page.check('#agree');
+    await page.click('button[type="submit"]');
+
+    await expect(page.locator('#contact-success')).toBeVisible({ timeout: 15_000 });
+    await expect(page.locator('#contact-success')).toContainText('접수되었습니다');
+  });
 });

tests/e2e/login-test.spec.ts

@@ -4,6 +4,21 @@ const baseUrl = 'https://www.taxbaik.com/taxbaik';
 const username = 'test_admin';
 const password = 'TestAdmin@123456';
 
+test('Admin Login Page - prerendered HTML contains the form before JS runs', async ({ request }) => {
+  // Login.razor is @rendermode ...(prerender: true), so the raw HTTP response
+  // (no JS execution) must already contain the login form markup. This is the
+  // regression check for the WASM-boot white-screen bug: if Router/Routes ever
+  // regains a global @rendermode, this prerender is silently dropped and this
+  // test catches it without needing a browser.
+  const response = await request.get(`${baseUrl}/admin/login`);
+  expect(response.ok()).toBeTruthy();
+
+  const html = await response.text();
+  expect(html).toContain('name="username"');
+  expect(html).toContain('name="password"');
+  expect(html).toContain('admin-login-form');
+});
+
 test('Admin Login Page - Full Flow Test', async ({ page }) => {
   // 콘솔 에러 캡처
   page.on('console', msg => {