Migrate SiteSettings controller to FastEndpoints

Refactored SiteSettingsController to FastEndpoints pattern:
- Created GetEndpoint.cs: GET /api/sitesettings (authorized)
- Created SaveEndpoint.cs: PUT /api/sitesettings (authorized)
- Removed legacy SiteSettingsController.cs

Both endpoints use Bearer token authentication and are auto-discovered
by FastEndpoints configuration in Program.cs.

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

src/TaxBaik.Web/Endpoints/SiteSettings/GetEndpoint.cs

@@ -0,0 +1,26 @@
+using FastEndpoints;
+using TaxBaik.Application.Services;
+
+namespace TaxBaik.Web.Endpoints.SiteSettings;
+
+public class GetEndpoint : Endpoint<EmptyRequest, IReadOnlyDictionary<string, string>>
+{
+    private readonly SiteSettingService _siteSettingService;
+
+    public GetEndpoint(SiteSettingService siteSettingService)
+    {
+        _siteSettingService = siteSettingService;
+    }
+
+    public override void Configure()
+    {
+        Get("/api/sitesettings");
+        Policies("Bearer");
+    }
+
+    public override async Task HandleAsync(EmptyRequest _, CancellationToken ct)
+    {
+        var settings = await _siteSettingService.GetAllAsync(ct);
+        await SendAsync(settings, 200, cancellation: ct);
+    }
+}

src/TaxBaik.Web/Endpoints/SiteSettings/SaveEndpoint.cs

@@ -0,0 +1,48 @@
+using FastEndpoints;
+using TaxBaik.Application.Services;
+
+namespace TaxBaik.Web.Endpoints.SiteSettings;
+
+public class SaveSiteSettingsRequest
+{
+    public string Phone { get; set; } = string.Empty;
+    public string Email { get; set; } = string.Empty;
+    public string KakaoUrl { get; set; } = string.Empty;
+    public string InstagramUrl { get; set; } = string.Empty;
+}
+
+public class SaveResponse
+{
+    public string Message { get; set; } = string.Empty;
+}
+
+public class SaveEndpoint : Endpoint<SaveSiteSettingsRequest, SaveResponse>
+{
+    private readonly SiteSettingService _siteSettingService;
+
+    public SaveEndpoint(SiteSettingService siteSettingService)
+    {
+        _siteSettingService = siteSettingService;
+    }
+
+    public override void Configure()
+    {
+        Put("/api/sitesettings");
+        Policies("Bearer");
+    }
+
+    public override async Task HandleAsync(SaveSiteSettingsRequest request, CancellationToken ct)
+    {
+        if (request == null)
+        {
+            ThrowError("요청 본문이 비어 있습니다.");
+        }
+
+        await _siteSettingService.SaveAsync(request.Phone, request.Email, request.KakaoUrl, request.InstagramUrl, ct);
+
+        await SendAsync(new SaveResponse
+        {
+            Message = "사이트 설정이 저장되었습니다."
+        }, 200, cancellation: ct);
+    }
+}