docs: update media item bruno docs with normalization info

Update Update Media Item.bru to document normalization behavior:
- Note that tags and contributors are auto-normalized (same as Create)
- Document response includes updated search fields

Relates to Tags & Contributors Migration documentation updates

docs/developer/api/media-items/get_media_item.md

@@ -37,10 +37,13 @@ Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
   "file_size": 1024000,
   "mime_type": "application/epub+zip",
   "cover_image_path": "/path/to/cover.jpg",
-  "series": "Series Name",
-  "series_number": 1,
-  "tags": "sci-fi, space opera",
-  "language": "en",
+   "series": "Series Name",
+   "series_number": 1,
+   "tags": ["sci-fi", "space opera"],
+   "tags_search": ["sci fi", "space opera"],
+   "contributors": ["Author Name", "ACME CORP."],
+   "contributors_search": ["author name", "acme corp"],
+   "language": "en",
   "page_count": 350,
   "genre": "Science Fiction",
   "copyright_year": 2023,