docs: unify documentation and streamline code comments

- Translated project documentation (LEARNING-JOURNEY, CONTRIBUTORS, AI_DISCLOSURE) to English for better accessibility.
- Standardized internal code documentation by converting XML-doc blocks to standard comment format.
- Cleaned up inline comments and removed redundant versioning metadata across the codebase.
- Refactored non-functional text elements to improve readability and maintain a consistent style.

HellionChat/Export/MessageExporter.cs

@@ -32,12 +32,8 @@ internal static class ExportFormatExt
         };
 }
 
-/// <summary>
-/// Serializes message snapshots into Markdown, JSON, or CSV. The caller is
-/// expected to filter the input enumerable; this class only handles
-/// formatting and writes to the supplied path. Sender substring filtering
-/// happens here because it requires deserialized SeString.TextValue.
-/// </summary>
+// Serializes message snapshots to Markdown, JSON, or CSV.
+// Caller handles pre-filtering except sender substring, which requires deserialized SeString.TextValue.
 internal static class MessageExporter
 {
     internal record FilterDescription(
@@ -100,6 +96,7 @@ internal static class MessageExporter
             var chatType = (ChatType)(ushort)m.Code.Type;
             var sender = m.SenderSource.TextValue.Trim().Trim('<', '>', '[', ']', ':').Trim();
             var content = m.ContentSource.TextValue;
+
             if (string.IsNullOrEmpty(sender))
                 w.WriteLine($"**[{localDate:HH:mm}] {chatType}:** {content}");
             else
@@ -132,8 +129,7 @@ internal static class MessageExporter
         FilterDescription filter
     )
     {
-        // Manual JSON to avoid pulling in System.Text.Json policy choices.
-        // Output is a single object with metadata and an array of messages.
+        // Manual JSON to avoid System.Text.Json policy coupling.
         w.Write("{\n  \"exported_at\": \"");
         w.Write(DateTimeOffset.UtcNow.ToString("O", CultureInfo.InvariantCulture));
         w.Write("\",\n  \"plugin\": \"Hellion Chat\",\n");
@@ -194,7 +190,7 @@ internal static class MessageExporter
         FilterDescription filter
     )
     {
-        // Header line always written so empty exports are still importable.
+        // Header always written so empty exports remain importable.
         w.WriteLine("Date,ChatType,ChatTypeName,Sender,Content,Receiver,ContentId");
         var count = 0;
         foreach (var m in messages)