Use CultureInfo.InvariantCulture for date formatting

Added System.Globalization namespace and updated date formatting
to use CultureInfo.InvariantCulture in CreatePostCommand.cs,
UpdatePostCommand.cs, and Seed.cs. This ensures consistent
date string formatting across different cultures.

src/Moonglade.Core/PostFeature/CreatePostCommand.cs

@@ -1,4 +1,5 @@
-using Microsoft.Extensions.Configuration;
+using System.Globalization;
+using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.Logging;
 using Moonglade.Configuration;
 using Moonglade.Data;
@@ -53,7 +54,7 @@ public async Task<PostEntity> Handle(CreatePostCommand request, CancellationToke
             IsOutdated = request.Payload.IsOutdated,
         };
 
-        post.RouteLink = $"{post.PubDateUtc.GetValueOrDefault():yyyy/M/d}/{request.Payload.Slug}";
+        post.RouteLink = $"{post.PubDateUtc.GetValueOrDefault().ToString("yyyy/M/d", CultureInfo.InvariantCulture)}/{request.Payload.Slug}";
 
         // check if exist same slug under the same day
         var todayUtc = DateTime.UtcNow.Date;

src/Moonglade.Core/PostFeature/UpdatePostCommand.cs

@@ -6,6 +6,7 @@
 using Moonglade.Data;
 using Moonglade.Data.Specifications;
 using Moonglade.Utils;
+using System.Globalization;
 
 namespace Moonglade.Core.PostFeature;
 
@@ -92,7 +93,7 @@ public async Task<PostEntity> Handle(UpdatePostCommand request, CancellationToke
         post.IsFeatured = postEditModel.Featured;
         post.HeroImageUrl = string.IsNullOrWhiteSpace(postEditModel.HeroImageUrl) ? null : Helper.SterilizeLink(postEditModel.HeroImageUrl);
         post.IsOutdated = postEditModel.IsOutdated;
-        post.RouteLink = $"{post.PubDateUtc.GetValueOrDefault():yyyy/M/d}/{postEditModel.Slug}";
+        post.RouteLink = $"{post.PubDateUtc.GetValueOrDefault().ToString("yyyy/M/d", CultureInfo.InvariantCulture)}/{postEditModel.Slug}";
 
         // 1. Add new tags to tag lib
         var tags = string.IsNullOrWhiteSpace(postEditModel.Tags) ?

src/Moonglade.Data/Seed.cs

@@ -1,5 +1,6 @@
 using Microsoft.Extensions.Logging;
 using Moonglade.Data.Entities;
+using System.Globalization;
 
 namespace Moonglade.Data;
 
@@ -48,7 +49,7 @@ public static async Task SeedAsync(BlogDbContext dbContext, ILogger logger, int
                 ContentLanguageCode = "en-us",
                 Tags = dbContext.Tag.ToList(),
                 PostCategory = dbContext.PostCategory.ToList(),
-                RouteLink = $"{DateTime.UtcNow:yyyy/M/d}/welcome-to-moonglade"
+                RouteLink = $"{DateTime.UtcNow.ToString("yyyy/M/d", CultureInfo.InvariantCulture)}/welcome-to-moonglade"
             };
 
             await dbContext.Post.AddAsync(post);