Replace file-based blog with API-backed service

BlogService now fetches from Media.JoshHeaps.Net API via HttpClient
with in-memory caching (5-min TTL) and stale cache fallback.
Removed Markdig/YamlDotNet dependencies. All page models now async.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

JoshHeaps.Net/Services/Implementations/BlogService.cs

@@ -0,0 +1,88 @@
+using System.Collections.Concurrent;
+using System.Text.Json;
+using JoshHeaps.Net.Models;
+using JoshHeaps.Net.Services.Interfaces;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+public class BlogService : IBlogService
+{
+    private readonly HttpClient _httpClient;
+    private readonly ILogger<BlogService> _logger;
+    private readonly TimeSpan _cacheTtl = TimeSpan.FromMinutes(5);
+
+    private readonly ConcurrentDictionary<string, CacheEntry> _cache = new();
+
+    private static readonly JsonSerializerOptions JsonOptions = new()
+    {
+        PropertyNameCaseInsensitive = true
+    };
+
+    public BlogService(IHttpClientFactory httpClientFactory, ILogger<BlogService> logger)
+    {
+        _httpClient = httpClientFactory.CreateClient("BlogApi");
+        _logger = logger;
+    }
+
+    public async Task<List<BlogPost>> GetAllPostsAsync()
+    {
+        return await GetCachedAsync("all_posts",
+            () => FetchAsync<List<BlogPost>>("api/blog/posts")) ?? [];
+    }
+
+    public async Task<BlogPost?> GetPostBySlugAsync(string slug)
+    {
+        return await GetCachedAsync($"post_{slug}",
+            () => FetchAsync<BlogPost>($"api/blog/posts/{Uri.EscapeDataString(slug)}"));
+    }
+
+    public async Task<List<BlogPost>> GetPostsByTagAsync(string tag)
+    {
+        return await GetCachedAsync($"tag_{tag}",
+            () => FetchAsync<List<BlogPost>>($"api/blog/posts/tags/{Uri.EscapeDataString(tag)}")) ?? [];
+    }
+
+    private async Task<T?> FetchAsync<T>(string path) where T : class
+    {
+        try
+        {
+            var response = await _httpClient.GetAsync(path);
+            if (!response.IsSuccessStatusCode)
+            {
+                _logger.LogWarning("Blog API returned {StatusCode} for {Path}", response.StatusCode, path);
+                return null;
+            }
+
+            var json = await response.Content.ReadAsStringAsync();
+            return JsonSerializer.Deserialize<T>(json, JsonOptions);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to fetch from blog API: {Path}", path);
+            return null;
+        }
+    }
+
+    private async Task<T?> GetCachedAsync<T>(string key, Func<Task<T?>> factory) where T : class
+    {
+        if (_cache.TryGetValue(key, out var entry) && entry.ExpiresAt > DateTime.UtcNow)
+            return (T?)entry.Value;
+
+        var result = await factory();
+
+        if (result is not null)
+        {
+            _cache[key] = new CacheEntry(result, DateTime.UtcNow.Add(_cacheTtl));
+        }
+        else if (entry is not null)
+        {
+            // API unreachable — serve stale cache
+            _logger.LogWarning("Serving stale cache for key {Key}", key);
+            return (T?)entry.Value;
+        }
+
+        return result;
+    }
+
+    private record CacheEntry(object Value, DateTime ExpiresAt);
+}