Walk up ancestor nodes to find documentable node at cursor position

FindDocumentableNode now uses AncestorsAndSelf() so types where FindNode
returns a child node (EventField, ConversionOperator, etc.) correctly resolve
to their parent declaration. Existing types are unaffected since they match
on the first (self) check.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: d1820

CodeDocumentor2026/Commands/Context/CodeDocumentorEditorCommand.cs

@@ -1,5 +1,7 @@
 using System;
+using System.Collections.Generic;
 using System.ComponentModel.Design;
+using System.Linq;
 using System.Threading.Tasks;
 using CodeDocumentor.Common.Interfaces;
 using CodeDocumentor2026.Extensions;
@@ -331,13 +333,11 @@ private SyntaxNode FindDocumentableNode(SyntaxNode root, int line, int column)
                 // Find the node at the exact cursor position
                 var nodeAtPosition = root.FindNode(Microsoft.CodeAnalysis.Text.TextSpan.FromBounds(position, position));
 
-                // Use the service to determine if it's documentable - don't traverse up
-                if (_commentBuilderService.IsDocumentableNode(nodeAtPosition))
-                {
-                    return nodeAtPosition;
-                }
-
-                return null;
+                // Walk up from the found node to find the nearest documentable ancestor.
+                // AncestorsAndSelf() checks the node itself first, so existing behavior is preserved
+                // for types where FindNode already returns the declaration node directly.
+                return nodeAtPosition.AncestorsAndSelf()
+                    .FirstOrDefault(n => _commentBuilderService.IsDocumentableNode(n));
             }
             catch (Exception ex)
             {