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/downloads.js

@@ -2,6 +2,7 @@ import { defineStore } from 'pinia'
 import { ref } from 'vue'
 import { useApi } from '../composables/useApi.js'
 import { useAsyncAction } from '../composables/useAsyncAction.js'
+import { useInflightToken } from '../composables/useInflightToken.js'
 
 export const useDownloadsStore = defineStore('downloads', () => {
   const api = useApi()
@@ -22,6 +23,10 @@ export const useDownloadsStore = defineStore('downloads', () => {
   // the "active now" panel always reflects what's happening regardless of
   // how the operator has filtered the historical list below.
   const activeEvents = ref([])
+  // Filter changes (applyFilter) and rapid pagination can interleave
+  // responses; without an inflight guard the late response from a
+  // prior filter overwrites the current view. Audit 2026-06-02.
+  const inflight = useInflightToken()
 
   function _params(extra = {}) {
     const out = { limit: 50, ...extra }
@@ -32,8 +37,10 @@ export const useDownloadsStore = defineStore('downloads', () => {
   }
 
   async function loadFirst() {
+    const t = inflight.claim()
     await run(async () => {
       const body = await api.get('/api/downloads', { params: _params() })
+      if (!t.isCurrent()) return
       events.value = body
       cursor.value = body.length ? body[body.length - 1].id : null
       hasMore.value = body.length === 50
@@ -42,8 +49,10 @@ export const useDownloadsStore = defineStore('downloads', () => {
 
   async function loadMore() {
     if (!hasMore.value || cursor.value == null) return
+    const t = inflight.claim()
     await run(async () => {
       const body = await api.get('/api/downloads', { params: _params({ before: cursor.value }) })
+      if (!t.isCurrent()) return
       events.value.push(...body)
       cursor.value = body.length ? body[body.length - 1].id : cursor.value
       hasMore.value = body.length === 50
@@ -71,6 +80,9 @@ export const useDownloadsStore = defineStore('downloads', () => {
   }
 
   async function applyFilter(patch) {
+    // Drop any in-flight loadFirst/loadMore from the previous filter
+    // so its late response doesn't overwrite this filter's results.
+    inflight.cancel()
     filter.value = { ...filter.value, ...patch }
     await loadFirst()
   }