fix: resolve login page CSS styling issues

- Map /login route to static login.html file to serve embedded CSS correctly
- Redirect /login to /login.html for proper static file delivery
- Fix NavigationContext namespace ambiguity in App.razor (MudBlazor vs ASP.NET)
- Fix StatusCodePages middleware path validation (StartsWithSegments → StartsWith)

Login page now displays with:
- Gradient background with frosted glass card design
- Properly styled form inputs and validation
- Professional Material Design appearance
- Working client-side authentication flow

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

screenshot.mjs

@@ -0,0 +1,14 @@
+import { chromium } from '@playwright/test';
+
+(async () => {
+  try {
+    const browser = await chromium.launch();
+    const page = await browser.newPage({ viewport: { width: 1280, height: 720 } });
+    await page.goto('http://localhost:5265/login');
+    await page.screenshot({ path: './login-screenshot.png', fullPage: true });
+    console.log('✓ Screenshot saved to ./login-screenshot.png');
+    await browser.close();
+  } catch (e) {
+    console.error('Error:', e.message);
+  }
+})();