refactor(importer): archive tags drop kind prefix

Archive identifier string (artist:archive_name) stays as the tag's
opaque name — the archive kind lives in the kind column.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/utils/image_importer.py

@@ -946,30 +946,30 @@ def extract_archive_name(filename: str) -> str:
 
 def compute_archive_tag_name(artist: str, archive_filename: str) -> str:
     """
-    Generate an archive tag name in the format: 'archive:{artist}:{archive_name}'
+    Generate an archive tag name in the format: '{artist}:{archive_name}'
 
     Similar to post tags (post:{platform}:{artist}:{id}), archive tags use
     a consistent prefix and colon-separated components.
 
     Examples:
     - artist="InCaseArt", filename="43387617_attachment_83109081_October 2020 Rewards.rar"
-      -> "archive:InCaseArt:October 2020 Rewards"
+      -> "InCaseArt:October 2020 Rewards"
 
     If a tag with the same name already exists, appends a numeric suffix.
     """
     archive_name = extract_archive_name(archive_filename)
-    base_tag = f"archive:{artist}:{archive_name}"
+    base_name = f"{artist}:{archive_name}"
 
     # Check if tag already exists
-    existing = Tag.query.filter_by(name=base_tag, kind='archive').first()
+    existing = Tag.query.filter_by(kind='archive', name=base_name).first()
     if not existing:
-        return base_tag
+        return base_name
 
     # Tag exists, add numeric suffix
     n = 2
     while True:
-        candidate = f"{base_tag} ({n})"
-        if not Tag.query.filter_by(name=candidate, kind='archive').first():
+        candidate = f"{base_name} ({n})"
+        if not Tag.query.filter_by(kind='archive', name=candidate).first():
             return candidate
         n += 1
 
@@ -978,12 +978,12 @@ def compute_next_archive_tag_name(artist: str, width: int = ARCHIVE_NUM_WIDTH) -
     """
     DEPRECATED: Use compute_archive_tag_name() instead.
 
-    Return a unique incremental tag name like: 'archive:{artist}/0001', '0002', ...
-    - Looks only at Tag(kind='archive') with names starting 'archive:{artist}/'
+    Return a unique incremental tag name like: '{artist}/0001', '0002', ...
+    - Looks only at Tag(kind='archive') with names starting '{artist}/'
     - Finds max numeric suffix and returns next number (zero-padded).
     - Ensures no collision even if tags were renamed.
     """
-    prefix = f"archive:{artist}/"
+    prefix = f"{artist}/"
     # Pull existing tag names for this artist/prefix
     rows = (Tag.query
               .with_entities(Tag.name)