fix: restore Sitemap as Razor Page for search engine compatibility

Problem:
- SitemapEndpoint (FastEndpoints) creates /api/sitemap.xml
- robots.txt references /taxbaik/sitemap.xml
- Path mismatch breaks search engine crawling

Solution:
- Restore Sitemap.cshtml (Razor Page)
- Restore Sitemap.cshtml.cs (PageModel with BlogService)
- Remove SitemapEndpoint (FastEndpoints)
- Proper XML Content-Type handling
- Exact path match: /taxbaik/sitemap.xml

Why Razor Page?
- Razor Pages handle exact @page routes better
- Search engines know standard sitemap.xml paths
- No /api prefix routing conflicts
- Direct SSR rendering without endpoint routing

Verification for Google/Naver:
✓ /taxbaik/sitemap.xml (exact match with robots.txt)
✓ Content-Type: application/xml
✓ Valid XML structure
✓ Dynamic blog posts included

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

src/TaxBaik.Web/Endpoints/SitemapEndpoint.cs

@@ -1,61 +0,0 @@
-using FastEndpoints;
-using TaxBaik.Application.Services;
-
-namespace TaxBaik.Web.Endpoints;
-
-/// <summary>
-/// GET /api/sitemap.xml - 동적 사이트맵 생성
-/// 블로그 포스트, FAQ, 공지사항 포함
-/// </summary>
-public class SitemapEndpoint : EndpointWithoutRequest<string>
-{
-    private readonly BlogService _blogService;
-
-    public SitemapEndpoint(BlogService blogService)
-    {
-        _blogService = blogService;
-    }
-
-    public override void Configure()
-    {
-        Get("/sitemap.xml");
-        AllowAnonymous();
-    }
-
-    public override async Task<string> ExecuteAsync(CancellationToken ct)
-    {
-        var baseUrl = "https://www.taxbaik.com/taxbaik";
-        var urls = new List<string>
-        {
-            // 정적 페이지
-            $"{baseUrl}",
-            $"{baseUrl}/about",
-            $"{baseUrl}/services",
-            $"{baseUrl}/contact",
-            $"{baseUrl}/privacy",
-            $"{baseUrl}/terms",
-            $"{baseUrl}/blog",
-            $"{baseUrl}/faq",
-            $"{baseUrl}/announcement",
-            $"{baseUrl}/inquiry"
-        };
-
-        // 동적 블로그 포스트
-        var (posts, _) = await _blogService.GetPublishedPagedAsync(1, 1000, categoryId: null, ct: ct);
-        foreach (var post in posts)
-        {
-            urls.Add($"{baseUrl}/blog/{post.Slug}");
-        }
-
-        // XML 생성
-        var now = DateTime.UtcNow.ToString("yyyy-MM-dd");
-        var urlEntries = string.Join("\n", urls.Select(url =>
-            $"    <url>\n        <loc>{System.Net.WebUtility.HtmlEncode(url)}</loc>\n        <lastmod>{now}</lastmod>\n    </url>"));
-
-        var xml = $"<?xml version=\"1.0\" encoding=\"utf-8\"?>\n<urlset xmlns=\"http://www.sitemaps.org/schemas/sitemap/0.9\">\n{urlEntries}\n</urlset>";
-
-        // XML Content-Type 설정
-        HttpContext.Response.ContentType = "application/xml; charset=utf-8";
-        return xml;
-    }
-}

src/TaxBaik.Web/Pages/Sitemap.cshtml

@@ -0,0 +1,14 @@
+@page "/sitemap.xml"
+@model TaxBaik.Web.Pages.SitemapModel
+@{
+    Response.ContentType = "application/xml; charset=utf-8";
+}<?xml version="1.0" encoding="utf-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+    @foreach (var url in Model.Urls)
+    {
+        <url>
+            <loc>@System.Net.WebUtility.HtmlEncode(url)</loc>
+            <lastmod>@DateTime.UtcNow:yyyy-MM-dd</lastmod>
+        </url>
+    }
+</urlset>

src/TaxBaik.Web/Pages/Sitemap.cshtml.cs

@@ -0,0 +1,43 @@
+using Microsoft.AspNetCore.Mvc.RazorPages;
+using TaxBaik.Application.Services;
+
+namespace TaxBaik.Web.Pages;
+
+public class SitemapModel : PageModel
+{
+    private readonly BlogService _blogService;
+
+    public List<string> Urls { get; set; } = [];
+
+    public SitemapModel(BlogService blogService)
+    {
+        _blogService = blogService;
+    }
+
+    public async Task OnGetAsync()
+    {
+        var baseUrl = "https://www.taxbaik.com/taxbaik";
+
+        // 정적 페이지
+        Urls.AddRange(new[]
+        {
+            $"{baseUrl}",
+            $"{baseUrl}/about",
+            $"{baseUrl}/services",
+            $"{baseUrl}/contact",
+            $"{baseUrl}/privacy",
+            $"{baseUrl}/terms",
+            $"{baseUrl}/blog",
+            $"{baseUrl}/faq",
+            $"{baseUrl}/announcement",
+            $"{baseUrl}/inquiry"
+        });
+
+        // 동적 블로그 포스트
+        var (posts, _) = await _blogService.GetPublishedPagedAsync(1, 1000, categoryId: null, ct: default);
+        foreach (var post in posts)
+        {
+            Urls.Add($"{baseUrl}/blog/{post.Slug}");
+        }
+    }
+}