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>

frontend/src/stores/explore.js

@@ -44,7 +44,9 @@ export const useExploreStore = defineStore('explore', () => {
       // empty and let the view explain why (anchor.has_embedding === false).
       if (detail.has_embedding) {
         const body = await api.get('/api/gallery/similar', {
-          params: { similar_to: numId, limit: NEIGHBOR_LIMIT },
+          // exclude_wip: keep work-in-progress out of the Explore rabbit-hole
+          // (the gallery's own "similar" button still shows it) — operator 2026-07-08.
+          params: { similar_to: numId, limit: NEIGHBOR_LIMIT, exclude_wip: 1 },
         })
         if (!t.isCurrent()) return
         neighbors.value = body.images || []