fix(audit-g2): async race / state-leak across eight stores

Extracts gallery.js's hand-rolled inflightId pattern into a new
useInflightToken composable; adopts in every store that previously
had no guard against late-response overwrites or wrong-image URL
interpolation.

Two operator-impacting bugs the audit (workflow wf_bbe3fdb1-e62)
flagged:

- modal.removeTag rolled back the chip rail unconditionally even
  when only the secondary dismiss POST had failed — UI lied until
  refresh. And all tag-mutation URLs interpolated currentImageId
  AFTER an await, so a fast prev/next could route DELETE/POST to
  the wrong image. Both fixed: split try/catch (dismiss failure
  surfaces a warning, doesn't roll back the delete); imageId
  captured at call-time and used in URLs throughout.

- suggestions.accept dereferenced currentImageId after the awaited
  POST /api/tags, so the subsequent /suggestions/accept could
  apply A's chosen tag to image B AND push it to B's allowlist.
  Fixed by capturing imageId at click-time + inflight guard on
  load().

Same shape across artist / downloads / artistDirectory /
tagDirectory / posts stores: rapid filter/nav changes used to
interleave responses (last-writer-wins). Now the late response is
discarded and the most-recent request wins. Filter-change-during-
search no longer drops the second fetch because the loading flag
was still true from the first.

gallery.js's inflightId removed in favor of the shared composable
so the pattern stays consistent.

frontend/src/stores/gallery.js

@@ -1,6 +1,7 @@
 import { defineStore } from 'pinia'
 import { ref, computed } from 'vue'
 import { useApi } from '../composables/useApi.js'
+import { useInflightToken } from '../composables/useInflightToken.js'
 
 // Operator-confirmed 2026-05-30: fetch PAGE-sized chunks instead of one
 // 50-item request so items render as each batch lands. Total initial
@@ -22,9 +23,12 @@ export const useGalleryStore = defineStore('gallery', () => {
   const timelineBuckets = ref([])
   const timelineLoading = ref(false)
 
-  let inflightId = 0
+  // Was a hand-rolled inflightId counter; the audit-2026-06-02 fan-out
+  // moved this pattern into useInflightToken so every store can share it.
+  const inflight = useInflightToken()
 
   async function loadInitial() {
+    inflight.cancel()
     images.value = []
     dateGroups.value = []
     nextCursor.value = null
@@ -41,19 +45,19 @@ export const useGalleryStore = defineStore('gallery', () => {
     if (loading.value) return
     loading.value = true
     error.value = null
-    const myId = ++inflightId
+    const t = inflight.claim()
     try {
       const params = { limit: PAGE, ...activeFilterParam() }
       if (nextCursor.value) params.cursor = nextCursor.value
       const body = await api.get('/api/gallery/scroll', { params })
-      if (myId !== inflightId) return  // stale response
+      if (!t.isCurrent()) return
       images.value.push(...body.images)
       dateGroups.value = mergeGroups(dateGroups.value, body.date_groups)
       nextCursor.value = body.next_cursor
     } catch (e) {
       error.value = e.message
     } finally {
-      if (myId === inflightId) loading.value = false
+      if (t.isCurrent()) loading.value = false
     }
   }
 
@@ -68,8 +72,14 @@ export const useGalleryStore = defineStore('gallery', () => {
   }
 
   async function jumpTo(year, month) {
+    // Rapid timeline-jump clicks need the same race guard as
+    // loadMore — first jump's late body could clobber the second
+    // jump's already-applied state.
+    inflight.cancel()
+    const t = inflight.claim()
     const params = { year, month, ...activeFilterParam() }
     const body = await api.get('/api/gallery/jump', { params })
+    if (!t.isCurrent()) return
     if (body.cursor) {
       images.value = []
       dateGroups.value = []