feat(explore): exclude WIP-tagged work from the Explore rabbit-hole

Explore's neighbour grid (/api/gallery/similar → gallery_service.similar) now
takes an Explore-only exclude_wip flag that drops `wip` system-tagged images
from the candidates, alongside the banner/editor presentation tags. The
gallery's own "similar" button is unchanged (keeps wip, #1274) — only the
Explore store passes exclude_wip=1. The anchor itself may still be a WIP; only
neighbours are filtered.

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

backend/app/services/gallery_service.py

@@ -31,7 +31,7 @@ from ..models import (
     Tag,
     TagPositiveConfirmation,
 )
-from ..models.tag import PRESENTATION_SYSTEM_TAGS, image_tag
+from ..models.tag import PRESENTATION_SYSTEM_TAGS, WIP_SYSTEM_TAG, image_tag
 from .pagination import decode_cursor, encode_cursor
 from .tag_query import (
     fandom_join_alias,
@@ -715,6 +715,7 @@ class GalleryService:
         platform: str | None = None,
         untagged: bool = False, no_artist: bool = False,
         date_from: datetime | None = None, date_to: datetime | None = None,
+        exclude_wip: bool = False,
     ) -> list[GalleryImage] | None:
         """Visual "more like this": images near `image_id`'s SigLIP embedding
         (pgvector, HNSW-indexed — alembic 0036), then DIVERSIFIED so the result
@@ -751,14 +752,18 @@ class GalleryService:
         # Presentation images (banner / editor-screenshot system tags, #128)
         # cluster on UI chrome rather than content, so near any one of them
         # they'd fill the grid. Excluded from CANDIDATES only — the anchor
-        # itself may be a banner, and `wip` stays surfaced (real art; only
-        # the training pipelines exclude it).
+        # itself may be a banner. `wip` stays surfaced here by default (real art;
+        # only the training pipelines exclude it), but the Explore rabbit-hole
+        # passes exclude_wip to also drop work-in-progress (operator, 2026-07-08).
+        excluded_system_tags = PRESENTATION_SYSTEM_TAGS
+        if exclude_wip:
+            excluded_system_tags = (*PRESENTATION_SYSTEM_TAGS, WIP_SYSTEM_TAG)
         presentation = (
             select(image_tag.c.image_record_id)
             .join(Tag, Tag.id == image_tag.c.tag_id)
             .where(
                 Tag.is_system.is_(True),
-                Tag.name.in_(PRESENTATION_SYSTEM_TAGS),
+                Tag.name.in_(excluded_system_tags),
             )
         )
         stmt = stmt.where(