feat: add RSS/Atom feed support - fix Razor XML rendering

Changes:
- Rss.cshtml: Fixed Razor/XML syntax by using StringBuilder
- Feed.cshtml: Alias for /feed.xml
- Both pages use RssModel (BlogService)
- robots.txt: Added feed references

Fix:
- Removed @page duplicate directive
- Used StringBuilder for proper XML generation
- Avoided Razor XML tag nesting issues
- Both /rss.xml and /feed.xml now available

URLs:
✓ https://www.taxbaik.com/taxbaik/rss.xml
✓ https://www.taxbaik.com/taxbaik/feed.xml

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

src/TaxBaik.Web/Pages/Feed.cshtml

@@ -0,0 +1,35 @@
+@page "/feed.xml"
+@model TaxBaik.Web.Pages.RssModel
+@{
+    Response.ContentType = "application/rss+xml; charset=utf-8";
+}@{
+    var rssContent = new System.Text.StringBuilder();
+    rssContent.AppendLine("<?xml version=\"1.0\" encoding=\"utf-8\"?>");
+    rssContent.AppendLine("<rss version=\"2.0\" xmlns:content=\"http://purl.org/rss/1.0/modules/content/\">");
+    rssContent.AppendLine("  <channel>");
+    rssContent.AppendLine("    <title>백원숙 세무회계 - 블로그</title>");
+    rssContent.AppendLine("    <link>https://www.taxbaik.com/taxbaik</link>");
+    rssContent.AppendLine("    <description>세무사 백원숙의 세금, 부동산, 가족자산 전문 블로그</description>");
+    rssContent.AppendLine("    <language>ko-kr</language>");
+    rssContent.AppendLine($"    <lastBuildDate>{Model.LastBuildDate}</lastBuildDate>");
+    rssContent.AppendLine("    <ttl>60</ttl>");
+
+    foreach (var post in Model.Posts)
+    {
+        rssContent.AppendLine("    <item>");
+        rssContent.AppendLine($"      <title>{System.Net.WebUtility.HtmlEncode(post.Title)}</title>");
+        rssContent.AppendLine($"      <link>https://www.taxbaik.com/taxbaik/blog/{post.Slug}</link>");
+        rssContent.AppendLine($"      <guid isPermaLink=\"true\">https://www.taxbaik.com/taxbaik/blog/{post.Slug}</guid>");
+        rssContent.AppendLine($"      <pubDate>{post.PublishedAt?.ToString("R")}</pubDate>");
+        var desc = post.Content?.Substring(0, Math.Min(200, post.Content?.Length ?? 0)) ?? "";
+        rssContent.AppendLine($"      <description>{System.Net.WebUtility.HtmlEncode(desc)}</description>");
+        if (!string.IsNullOrEmpty(post.Content))
+        {
+            rssContent.AppendLine($"      <content:encoded><![CDATA[{post.Content}]]></content:encoded>");
+        }
+        rssContent.AppendLine("    </item>");
+    }
+
+    rssContent.AppendLine("  </channel>");
+    rssContent.AppendLine("</rss>");
+}@rssContent.ToString()

src/TaxBaik.Web/Pages/Rss.cshtml

@@ -0,0 +1,35 @@
+@page "/rss.xml"
+@model TaxBaik.Web.Pages.RssModel
+@{
+    Response.ContentType = "application/rss+xml; charset=utf-8";
+}@{
+    var rssContent = new System.Text.StringBuilder();
+    rssContent.AppendLine("<?xml version=\"1.0\" encoding=\"utf-8\"?>");
+    rssContent.AppendLine("<rss version=\"2.0\" xmlns:content=\"http://purl.org/rss/1.0/modules/content/\">");
+    rssContent.AppendLine("  <channel>");
+    rssContent.AppendLine("    <title>백원숙 세무회계 - 블로그</title>");
+    rssContent.AppendLine("    <link>https://www.taxbaik.com/taxbaik</link>");
+    rssContent.AppendLine("    <description>세무사 백원숙의 세금, 부동산, 가족자산 전문 블로그</description>");
+    rssContent.AppendLine("    <language>ko-kr</language>");
+    rssContent.AppendLine($"    <lastBuildDate>{Model.LastBuildDate}</lastBuildDate>");
+    rssContent.AppendLine("    <ttl>60</ttl>");
+
+    foreach (var post in Model.Posts)
+    {
+        rssContent.AppendLine("    <item>");
+        rssContent.AppendLine($"      <title>{System.Net.WebUtility.HtmlEncode(post.Title)}</title>");
+        rssContent.AppendLine($"      <link>https://www.taxbaik.com/taxbaik/blog/{post.Slug}</link>");
+        rssContent.AppendLine($"      <guid isPermaLink=\"true\">https://www.taxbaik.com/taxbaik/blog/{post.Slug}</guid>");
+        rssContent.AppendLine($"      <pubDate>{post.PublishedAt?.ToString("R")}</pubDate>");
+        var desc = post.Content?.Substring(0, Math.Min(200, post.Content?.Length ?? 0)) ?? "";
+        rssContent.AppendLine($"      <description>{System.Net.WebUtility.HtmlEncode(desc)}</description>");
+        if (!string.IsNullOrEmpty(post.Content))
+        {
+            rssContent.AppendLine($"      <content:encoded><![CDATA[{post.Content}]]></content:encoded>");
+        }
+        rssContent.AppendLine("    </item>");
+    }
+
+    rssContent.AppendLine("  </channel>");
+    rssContent.AppendLine("</rss>");
+}@rssContent.ToString()

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

@@ -0,0 +1,27 @@
+using Microsoft.AspNetCore.Mvc.RazorPages;
+using TaxBaik.Application.Services;
+using TaxBaik.Domain.Entities;
+
+namespace TaxBaik.Web.Pages;
+
+public class RssModel : PageModel
+{
+    private readonly BlogService _blogService;
+
+    public List<BlogPost> Posts { get; set; } = [];
+    public string LastBuildDate { get; set; } = DateTime.UtcNow.ToString("R");
+
+    public RssModel(BlogService blogService)
+    {
+        _blogService = blogService;
+    }
+
+    public async Task OnGetAsync()
+    {
+        // 최근 50개 블로그 포스트 (RSS는 일반적으로 최신 기사만 포함)
+        var (posts, _) = await _blogService.GetPublishedPagedAsync(1, 50, categoryId: null, ct: default);
+        Posts = posts.OrderByDescending(p => p.PublishedAt).ToList();
+
+        LastBuildDate = Posts.FirstOrDefault()?.PublishedAt?.ToString("R") ?? DateTime.UtcNow.ToString("R");
+    }
+}

src/TaxBaik.Web/Pages/_Layout.cshtml

@@ -28,6 +28,10 @@
     <meta name="theme-color" content="#C89D6E" />
     <link rel="icon" type="image/svg+xml" href="/taxbaik/favicon.svg" />
     <link rel="alternate icon" href="/taxbaik/favicon.ico" />
+
+    <!-- RSS Feed -->
+    <link rel="alternate" type="application/rss+xml" title="백원숙 세무회계 블로그" href="/taxbaik/rss.xml" />
+    <link rel="alternate" type="application/rss+xml" title="TaxBaik Blog Feed" href="/taxbaik/feed.xml" />
     <link rel="preconnect" href="https://fonts.googleapis.com" />
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
     <link rel="dns-prefetch" href="https://cdn.jsdelivr.net" />

src/TaxBaik.Web/wwwroot/robots.txt

@@ -30,4 +30,7 @@ Allow: /
 # Sitemap 위치
 Sitemap: https://www.taxbaik.com/taxbaik/sitemap.xml
 Sitemap: https://taxbaik.com/taxbaik/sitemap.xml
-Sitemap: https://www.taxbaik.com/taxbaik/robots.txt
+
+# RSS 피드
+Sitemap: https://www.taxbaik.com/taxbaik/rss.xml
+Sitemap: https://www.taxbaik.com/taxbaik/feed.xml