feat: implement data migration service to convert ANSI escape codes to printable color tags

src/EchoHub.Server/Setup/DataMigrationService.cs

@@ -0,0 +1,78 @@
+using System.Text.RegularExpressions;
+using EchoHub.Server.Data;
+using Microsoft.EntityFrameworkCore;
+
+namespace EchoHub.Server.Setup;
+
+public static partial class DataMigrationService
+{
+    public static async Task RunAsync(IServiceProvider services)
+    {
+        using var scope = services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<EchoHubDbContext>();
+        var logger = scope.ServiceProvider.GetRequiredService<ILoggerFactory>()
+            .CreateLogger("EchoHub.Server.Setup.DataMigration");
+
+        await MigrateAnsiMessagesAsync(db, logger);
+    }
+
+    private static async Task MigrateAnsiMessagesAsync(EchoHubDbContext db, ILogger logger)
+    {
+        // Load messages that contain the ESC byte (0x1B) — these have legacy ANSI color codes.
+        // Filter by Image type first (only images have ANSI art), then check content in memory.
+        var messages = await db.Messages
+            .Where(m => m.Type == Core.Models.MessageType.Image)
+            .ToListAsync();
+
+        var toMigrate = messages.Where(m => m.Content.Contains('\x1b')).ToList();
+
+        if (toMigrate.Count == 0)
+            return;
+
+        logger.LogInformation("Found {Count} messages with legacy ANSI color codes. Migrating to color tag format...", toMigrate.Count);
+
+        var modified = 0;
+        foreach (var message in toMigrate)
+        {
+            var converted = AnsiToColorTags(message.Content);
+            if (converted != message.Content)
+            {
+                message.Content = converted;
+                modified++;
+            }
+        }
+
+        if (modified > 0)
+        {
+            await db.SaveChangesAsync();
+            logger.LogInformation("Migrated {Count} messages from ANSI escape codes to printable color tags.", modified);
+        }
+    }
+
+    /// <summary>
+    /// Convert ANSI escape codes to printable color tags.
+    /// \x1b[38;2;R;G;Bm → {F:RRGGBB}, \x1b[48;2;R;G;Bm → {B:RRGGBB}, \x1b[0m → {X}
+    /// </summary>
+    public static string AnsiToColorTags(string text)
+    {
+        return AnsiColorRegex().Replace(text, match =>
+        {
+            if (match.Groups[1].Value == "0")
+                return "{X}";
+
+            if (match.Groups[2].Success)
+            {
+                var r = int.Parse(match.Groups[3].Value);
+                var g = int.Parse(match.Groups[4].Value);
+                var b = int.Parse(match.Groups[5].Value);
+                var type = match.Groups[2].Value == "38;2" ? "F" : "B";
+                return $"{{{type}:{r:X2}{g:X2}{b:X2}}}";
+            }
+
+            return match.Value;
+        });
+    }
+
+    [GeneratedRegex(@"\x1b\[(?:(0)|(?:(38;2|48;2);(\d{1,3});(\d{1,3});(\d{1,3})))m")]
+    private static partial Regex AnsiColorRegex();
+}

src/EchoHub.Server/Setup/DatabaseSetup.cs

@@ -16,6 +16,9 @@ public static class DatabaseSetup
 
         await MigrateAsync(db, logger);
         await SeedDefaultChannelAsync(db, logger);
+
+        // Run data migrations (e.g. ANSI → color tag format)
+        await DataMigrationService.RunAsync(services);
     }
 
     private static async Task MigrateAsync(EchoHubDbContext db, ILogger logger)