fix(aliases): store modal alias under raw model key + make aliases visible/manageable

The headline bug: aliases created from the modal NEVER resolved. Create
sent the normalized display name ('Sword', 'Uchiha Sasuke') while
resolution keys on the raw booru model key ('sword', 'uchiha_sasuke',
case-sensitive) — so the mapping was stored under a key nothing looks up,
and the prediction kept reappearing unaliased. The raw key wasn't even in
the /suggestions response, so the modal couldn't send it.

- Suggestion now carries raw_name (the model key an alias must use) and
  via_alias (surfaced via an operator alias); both serialized by the API.
- Modal alias-create sends raw_name, not display_name (the fix). Aliased
  suggestions show an 'alias' badge and a 'Remove alias' action; 'Treat as
  alias for…' is hidden for centroid hits (no model key) and already-aliased
  rows.
- Tag-side management: TagCard ⋮ → 'Aliases…' opens a dialog listing the
  model keys that fold into a tag, with remove (GET /api/tags/<id>/aliases +
  AliasService.list_for_tag). Creation stays in the modal suggestion flow.

Tests: full API round-trip locking the raw-key contract (raw_name exposed →
alias authored with it → resolves + via_alias on a later image);
list_for_tag (service + API); via_alias/raw_name on the existing service
suggestion tests. No migration.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/api/suggestions.py

@@ -37,6 +37,11 @@ async def get_suggestions(image_id: int):
                         "score": round(s.score, 4),
                         "source": s.source,
                         "creates_new_tag": s.creates_new_tag,
+                        # raw model key (alias is stored under this) + whether an
+                        # operator alias produced this suggestion — drive the
+                        # modal's "Treat as alias"/"Remove alias" affordances.
+                        "raw_name": s.raw_name,
+                        "via_alias": s.via_alias,
                     }
                     for s in items
                 ]

backend/app/api/tags.py

@@ -8,6 +8,7 @@ from ..extensions import get_session
 from ..models import Tag, TagKind
 from ..models.tag_allowlist import TagAllowlist
 from ..services.bulk_tag_service import BulkTagService
+from ..services.ml.aliases import AliasService
 from ..services.series_match_service import SeriesMatchService
 from ..services.series_service import SeriesError, SeriesService
 from ..services.tag_directory_service import TagDirectoryService
@@ -200,6 +201,25 @@ async def get_tag(tag_id: int):
         )
 
 
+@tags_bp.route("/tags/<int:tag_id>/aliases", methods=["GET"])
+async def list_tag_aliases(tag_id: int):
+    """Model keys that fold into this tag (tag-side alias view). Remove via the
+    shared DELETE /api/aliases/<string>/<category>."""
+    async with get_session() as session:
+        if await session.get(Tag, tag_id) is None:
+            return jsonify({"error": "tag not found"}), 404
+        rows = await AliasService(session).list_for_tag(tag_id)
+    return jsonify(
+        [
+            {
+                "alias_string": r.alias_string,
+                "alias_category": r.alias_category,
+            }
+            for r in rows
+        ]
+    )
+
+
 @tags_bp.route("/tags/<int:tag_id>", methods=["PATCH"])
 async def update_tag(tag_id: int):
     """Rename and/or re-fandom a tag. Body may carry `name` and/or