feat: add /raw route to blog posts for markdown output

OliverBooth/Pages/Blog/RawArticle.cshtml

@@ -0,0 +1,2 @@
+@page "/blog/{year:int}/{month:int}/{day:int}/{slug}/raw"
+@model OliverBooth.Pages.Blog.RawArticle

OliverBooth/Pages/Blog/RawArticle.cshtml.cs

@@ -0,0 +1,52 @@
+using Cysharp.Text;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+using OliverBooth.Data.Blog;
+using OliverBooth.Services;
+
+namespace OliverBooth.Pages.Blog;
+
+/// <summary>
+///     Represents the page model for the <c>RawArticle</c> page.
+/// </summary>
+public class RawArticle : PageModel
+{
+    private readonly BlogService _blogService;
+
+    /// <summary>
+    ///     Initializes a new instance of the <see cref="RawArticle" /> class.
+    /// </summary>
+    /// <param name="blogService">The <see cref="BlogService" />.</param>
+    public RawArticle(BlogService blogService)
+    {
+        _blogService = blogService;
+    }
+
+    /// <summary>
+    ///     Gets the requested blog post.
+    /// </summary>
+    /// <value>The requested blog post.</value>
+    public BlogPost Post { get; private set; } = null!;
+
+    public IActionResult OnGet(int year, int month, int day, string slug)
+    {
+        if (!_blogService.TryGetBlogPost(year, month, day, slug, out BlogPost? post))
+        {
+            Response.StatusCode = 404;
+            return NotFound();
+        }
+        
+        using Utf8ValueStringBuilder builder = ZString.CreateUtf8StringBuilder();
+        builder.AppendLine("# " + post.Title);
+        if (_blogService.TryGetAuthor(post, out Author? author))
+            builder.AppendLine($"Author: {author.Name}");
+        
+        builder.AppendLine($"Published: {post.Published:R}");
+        if (post.Updated.HasValue)
+            builder.AppendLine($"Updated: {post.Updated:R}");
+        
+        builder.AppendLine();
+        builder.AppendLine(post.Body);
+        return Content(builder.ToString(), "text/plain");
+    }
+}