refactor(tags): unify suggestion source — one canonical DB-tag dropdown, drop dead raw/alias machinery (#154)

Every tag suggestion is a canonical DB tag now (tagging-v2 #114: heads + CCIP
score EXISTING concept tags). The pre-heads apparatus for model-predicted tags
that didn't exist in the DB — creates_new_tag / raw_name / via_alias, the
/suggestions/alias endpoint + add_alias_and_accept, AliasPickerDialog, and the
store's aliasAccept/removeAlias — was dead and is removed.

The type-to-add dropdown was TWO row sources (server autocomplete + the image's
ML suggestions) merged with a dedup that dropped the %-bearing suggestion row
when the debounced server hit landed — the operator's "confidence % flickers
then vanishes". Now it's ONE list of DB-tag matches, each annotated with the
model's confidence (join by canonical_tag_id) when the tag was scored for this
image. No dedup, no flicker; picking a suggested tag still records acceptance
via TagPanel.findPending.

Single per-image fetch: score_image now reports above_threshold per row
(computed vs the head's own suggest cut, separate from the inclusion floor), so
the rail makes ONE min=0 request and derives the panel (above_threshold) and the
dropdown (all, text-filtered) client-side — the two /suggestions calls collapse
to one. Manual "Create 'X' as <kind>" (novel typed names) is unchanged; the
alias table + tag-side alias admin + auto-apply alias matching are untouched.

Tests: gate/serializer assertions updated (above_threshold; dropped dead-field
+ alias-endpoint checks); frontend spec seeds via the single load and covers the
byCategory/aboveByCategory split.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CgZP9v2otxVJymiYsnVuMy

backend/app/services/ml/allowlist.py

@@ -12,13 +12,11 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from ...models import TagSuggestionRejection
 from ...models.tag import image_tag
-from .aliases import AliasService
 
 
 class AllowlistService:
     def __init__(self, session: AsyncSession):
         self.session = session
-        self.aliases = AliasService(session)
 
     async def _apply_image_tag(self, image_id: int, tag_id: int, source: str):
         stmt = insert(image_tag).values(
@@ -41,18 +39,6 @@ class AllowlistService:
         await self._apply_image_tag(image_id, tag_id, source="ml_accepted")
         await self._clear_rejection(image_id, tag_id)
 
-    async def add_alias_and_accept(
-        self,
-        image_id: int,
-        alias_string: str,
-        alias_category: str,
-        canonical_tag_id: int,
-    ) -> None:
-        await self.aliases.create(
-            alias_string, alias_category, canonical_tag_id
-        )
-        await self.accept(image_id, canonical_tag_id)
-
     async def dismiss(self, image_id: int, tag_id: int) -> None:
         stmt = insert(TagSuggestionRejection).values(
             image_record_id=image_id, tag_id=tag_id