feat(tagging): title-based WIP auto-tagging (#1458)

Auto-apply the `wip` system tag to posts whose TITLE explicitly declares
work-in-progress ("WIP" / "work in progress") — a deterministic, high-precision
complement to the image-based ML `wip` head. WIP images are excluded from the
Explore/gallery browse, so honouring the artist's own label keeps unfinished
pieces out of the main browse.

- services/wip_title.py: precision-first token-anchored matcher (swipe/wiped
  never trip it) + sync apply helpers (source='wip_title', ON CONFLICT DO
  NOTHING, chunked under the psycopg param ceiling).
- importer: live hook on FRESH import only (never on deep-scan/supersede), so a
  manually-removed WIP tag is never re-applied by a routine re-scan.
- maintenance.backfill_wip_title_tags: operator-triggered back-catalogue sweep
  (coarse SQL prefilter + regex confirm, keyset-paginated). Deliberately NOT a
  beat — a periodic re-run would silently undo manual removals.
- ImportSettings.wip_title_tagging_enabled (default ON, migration 0085) gating
  the live hook; GET/PATCH + POST /settings/wip-title/scan.
- Settings UI: toggle + "Scan existing posts" button.
- Tests: pure matcher unit tests + integration (apply idempotency, backfill
  precision).

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

frontend/src/stores/import.js

@@ -16,6 +16,7 @@ export const useImportStore = defineStore('import', () => {
   const settings = ref(null)
   const settingsLoading = ref(false)
   const settingsError = ref(null)
+  const wipScanBusy = ref(false)
 
   async function loadSettings() {
     settingsLoading.value = true
@@ -40,8 +41,25 @@ export const useImportStore = defineStore('import', () => {
     }
   }
 
+  // Enqueue the back-catalogue WIP-title scan (task #1458). New imports are
+  // tagged live; this catches posts already in the library. Fire-and-forget —
+  // the sweep runs on the maintenance worker and its run shows in Activity.
+  async function scanWipTitles() {
+    wipScanBusy.value = true
+    try {
+      const r = await api.post('/api/settings/wip-title/scan')
+      toast({ text: 'Scanning existing posts for WIP titles…', type: 'success' })
+      return r
+    } catch (e) {
+      toast({ text: `WIP scan failed: ${e.message}`, type: 'error' })
+      throw e
+    } finally {
+      wipScanBusy.value = false
+    }
+  }
+
   return {
-    settings, settingsLoading, settingsError,
-    loadSettings, patchSettings,
+    settings, settingsLoading, settingsError, wipScanBusy,
+    loadSettings, patchSettings, scanWipTitles,
   }
 })