fix: improve login form field selection and extend playwright timeouts

Changes:
1. admin-session.js: Use name attribute selectors instead of placeholder
   - Changed: querySelector('input[placeholder="사용자명"]')
   - To: querySelector('input[name="username"]')
   - Reason: Placeholder selectors are fragile with DOM mutations

2. playwright.config.ts: Extend test timeouts for WASM boot
   - Test timeout: 120s → 180s
   - Expect timeout: 60s → 90s
   - Reason: Blazor WASM bundle takes 60-120s to boot in local dev

3. tests/e2e/admin-login.spec.ts: Increase assertion timeouts
   - Dashboard heading visibility: 20s → 60s
   - Logout link visibility: timeout added 30s

4. tests/e2e/blog-crud.spec.ts: New comprehensive blog CRUD test
   - Tests complete login flow
   - Validates localStorage token storage
   - Checks blog list page navigation

Status: Login form submission now works with proper field selection.
Remaining: Blazor WASM boot optimization needed for production.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

tests/e2e/admin-login.spec.ts

@@ -73,8 +73,9 @@ test.describe('admin authentication', () => {
     }
 
     await expect(page).toHaveURL(/\/taxbaik\/admin\/dashboard$/, { timeout: 20_000 });
-    await expect(page.getByRole('heading', { name: '대시보드' }).first()).toBeVisible({ timeout: 20_000 });
-    await expect(page.getByRole('link', { name: /로그아웃/ })).toBeVisible();
+    // WASM 부팅에 시간이 걸릴 수 있으므로 더 긴 타임아웃 사용
+    await expect(page.getByRole('heading', { name: '대시보드' }).first()).toBeVisible({ timeout: 60_000 });
+    await expect(page.getByRole('link', { name: /로그아웃/ })).toBeVisible({ timeout: 30_000 });
     expect(consoleErrors, 'browser console/page errors').toEqual([]);
   });
 });