File-Upload: Attachments-Tabelle, Base64-Speicherung, Frontend mit Drag&Drop/Paste/Preview, Error-Handling Fix

Endpoints/HistoryEndpoint.cs

@@ -18,6 +18,7 @@ public static class HistoryEndpoint
         app.MapPost("/api/archive", HandleArchive);
         app.MapGet("/api/archives", HandleListArchives);
         app.MapGet("/api/archive/{archiveId}", HandleGetArchive);
+        app.MapGet("/api/attachments/{messageId}", HandleGetAttachments);
     }
 
     private static async Task HandleHistory(HttpContext ctx, DatabaseService db)
@@ -89,6 +90,34 @@ public static class HistoryEndpoint
         await ctx.Response.WriteAsJsonAsync(archives);
     }
 
+    private static async Task HandleGetAttachments(HttpContext ctx, DatabaseService db)
+    {
+        var messageIdStr = ctx.Request.RouteValues["messageId"]?.ToString();
+        if (!long.TryParse(messageIdStr, out var messageId))
+        {
+            ctx.Response.StatusCode = 400;
+            return;
+        }
+
+        var attachments = await db.GetAttachments(messageId);
+        // Ohne Base64-Data zurückgeben (zu groß), stattdessen als separater Download
+        var result = new List<object>();
+        foreach (var att in attachments)
+        {
+            result.Add(new
+            {
+                att.Id,
+                att.MessageId,
+                att.Type,
+                att.MediaType,
+                att.FileName,
+                att.Data,
+                att.CreatedAt
+            });
+        }
+        await ctx.Response.WriteAsJsonAsync(result);
+    }
+
     private static async Task HandleGetArchive(HttpContext ctx, DatabaseService db)
     {
         var archiveId = ctx.Request.RouteValues["archiveId"]?.ToString();