feat: migrate AuthController to FastEndpoints Endpoints (Phase 1)

IMPLEMENTATION:
- Create 4 FastEndpoints Endpoint classes:
  - LoginEndpoint: POST /api/auth/login
  - RefreshTokenEndpoint: POST /api/auth/refresh
  - ChangePasswordEndpoint: POST /api/auth/change-password
  - ResetPasswordEndpoint: POST /api/auth/reset-password

- Backup AuthController.cs (no longer active)
- Add FastEndpoints.Endpoint<TRequest, TResponse> pattern
- Implement proper DI with AuthService injection
- Use Policies("Bearer") for authorization
- Proper error handling with ThrowError()

ARCHITECTURE:
- Start of Phase 1: Core Auth APIs
- Endpoints follow FastEndpoints conventions
- DTOs: LoginRequest, RefreshTokenRequest, ChangePasswordRequest, ResetPasswordRequest, TokenPairResponse, MessageResponse
- AllowAnonymous for login/refresh/reset
- Bearer policy for change-password

VERIFICATION:
✅ dotnet build: 0 errors, 0 warnings
✅ dotnet test: 26/26 passed
✅ FastEndpoints auto-discovery working (no endpoint errors)
✅ JWT validation passes

Next Phase: BlogController and remaining APIs

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

test_run/wwwroot/js/site.js

@@ -0,0 +1,24 @@
+function openKakao() {
+    const kakaoUrl = document.querySelector('[data-kakao-url]')?.dataset.kakaoUrl || '#';
+    if (kakaoUrl !== '#') {
+        window.open(kakaoUrl, '_blank');
+    } else {
+        alert('카카오톡 채널 URL이 설정되지 않았습니다.');
+    }
+}
+
+document.addEventListener('DOMContentLoaded', function() {
+    const navbar = document.querySelector('.navbar');
+    if (!navbar) {
+        return;
+    }
+
+    const setShadow = () => {
+        navbar.style.boxShadow = window.scrollY > 0
+            ? '0 2px 8px rgba(0,0,0,0.1)'
+            : '0 1px 3px rgba(0,0,0,0.1)';
+    };
+
+    setShadow();
+    window.addEventListener('scroll', setShadow, { passive: true });
+});