fix: Move NFOGuard comment to bottom with other fields

Moved the NFOGuard source comment from the top of the XML file to
just before our field additions at the bottom. This creates a clear
separation showing where NFOGuard's modifications begin.

Expected structure:
[existing rich metadata]
<!-- NFOGuard - Source: tmdb:digital -->
<uniqueid type="imdb" default="true">tt123</uniqueid>
<premiered>2024-08-20</premiered>
<dateadded>2024-08-20T00:00:00+00:00</dateadded>
<lockdata>true</lockdata>

core/nfo_manager.py

@@ -186,6 +186,10 @@ class NFOManager:
             # Now append ALL NFOGuard fields at the VERY END of the file
             # Create elements and explicitly append them to ensure they're at the bottom
             
+            # Add NFOGuard comment marker as the first of our additions
+            nfoguard_comment = ET.Comment(f" NFOGuard - Source: {source} ")
+            movie.append(nfoguard_comment)
+            
             # Add IMDb uniqueid at the end (after all existing content)
             uniqueid = ET.Element("uniqueid", type="imdb", default="true")
             uniqueid.text = imdb_id
@@ -220,23 +224,14 @@ class NFOManager:
                 lockdata.text = "true"
                 movie.append(lockdata)
             
-            # Add NFOGuard comment at the beginning
-            comment_text = f" Created by {self.manager_brand} - Source: {source} "
-            
             # Write file with proper formatting
             tree = ET.ElementTree(movie)
             ET.indent(tree, space="  ", level=0)
             
-            # Write to string first to add comment
+            # Write directly to file (comment is already embedded in XML)
-            import xml.etree.ElementTree as ET_temp
-            xml_str = ET.tostring(movie, encoding='unicode')
-            
-            # Add XML declaration and comment
-            full_xml = f'<?xml version="1.0" encoding="utf-8"?>\n<!--{comment_text}-->\n{xml_str}'
-            
-            # Write to file
             with open(nfo_path, 'w', encoding='utf-8') as f:
-                f.write(full_xml)
+                f.write('<?xml version="1.0" encoding="utf-8"?>\n')
+                tree.write(f, encoding='unicode', xml_declaration=False)
             
             print(f"✅ Successfully created/updated movie NFO: {nfo_path}")
             print(f"   IMDb ID: {imdb_id}, Date Added: {dateadded}, Source: {source}")