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>

tests/test_ml_suggestions.py

@@ -107,6 +107,9 @@ async def test_alias_resolution(db):
     assert chars[0].display_name == "Sasuke Uchiha"
     assert chars[0].canonical_tag_id == canonical.id
     assert chars[0].creates_new_tag is False
+    # Surfaced via an alias on the raw model key — the UI marks it + offers undo.
+    assert chars[0].via_alias is True
+    assert chars[0].raw_name == "uchiha_sasuke"
 
 
 @pytest.mark.asyncio
@@ -122,6 +125,9 @@ async def test_raw_tag_creates_new(db):
     # title-cased), not the raw vocab key.
     assert chars[0].display_name == "Brand New Tag"
     assert chars[0].creates_new_tag is True
+    # Not aliased, but the raw key is carried so the modal can author one.
+    assert chars[0].via_alias is False
+    assert chars[0].raw_name == "brand_new_tag"
     assert chars[0].canonical_tag_id is None