fix(secure-context): full audit — DestructiveConfirmModal.expectedTokenOverride + bulk-delete + min-dim use backend-computed tokens

Operator-flagged 2026-05-27: walk the whole project for the same shape
as the min-dim Delete-button silent failure (crypto.subtle TypeError
on plain HTTP). FC runs over plain HTTP per the homelab posture;
Secure-Context-gated browser APIs are undefined on the production
origin.

**Audit results across `frontend/src/`:**

  crypto.subtle.digest        — 2 sites:
    - MinDimensionCard (fixed 2026-05-27)
    - BulkEditorPanel (THIS FIX)
  navigator.clipboard         — 1 site, already guarded:
    - utils/clipboard.js writeText with execCommand fallback
  serviceWorker / mediaDevices / Push / Web USB|HID|Bluetooth|Serial /
  cookieStore / queryLocalFonts / WebAuthn / geolocation
                              — NOT USED, nothing to fix

  Extension scripts (background.js) use crypto.subtle but run from
  moz-extension:// which IS a Secure Context — left as-is.

**BulkEditorPanel double bug**

The bulk-delete UI on the gallery selection had been broken since
FC-3k shipped, in two ways:

1. `crypto.subtle.digest` swallowed TypeError on plain HTTP — modal
   never opened. Same symptom as min-dim.
2. Even on HTTPS, the modal's `kind="images-selection"` produced
   `delete-images-selection-<sha8>` while the backend expected
   `delete-images-<sha8>`. The two would never match.

Fix:

- Backend `/api/admin/images/bulk-delete` dry-run response now returns
  `confirm_token` (the canonical `delete-images-<sha8>` string).
  Integration test `test_bulk_delete_dry_run_returns_counts` pinned to
  assert the new field.
- DestructiveConfirmModal gains an `expectedTokenOverride` prop. When
  set, it bypasses the `${action}-${kind}-${runId}` formula and uses
  the explicit string. This decouples the UI label (`kind`) from the
  wire-format token (server-provided), so future endpoints can use a
  kind-specific label without their kind name leaking into the token.
- BulkEditorPanel passes `:expected-token-override="bulkProjected?.confirm_token"`
  — no client-side crypto, no kind-prefix mismatch.
- MinDimensionCard refactored to the same explicit pattern (was
  slicing the 8-char suffix off the backend's token and passing it
  through `runId`; now passes the full backend token via
  `expected-token-override` directly). Cleaner; one source of truth.

**Banked memory**

`feedback_no_secure_context_apis.md` documents the full table of
Secure-Context-gated APIs, which ones FC currently uses, and how each
is handled. Indexed in MEMORY.md. Sites for the audit also listed in
the memory for future drift-checking.

No other Secure-Context-gated APIs found in `frontend/src/`. The same
shape won't recur unless someone adds a new dependency on one — at
which point the banked memory should fire.

frontend/src/components/gallery/BulkEditorPanel.vue

@@ -74,7 +74,7 @@
       v-model="deleteModalOpen"
       action="delete"
       kind="images-selection"
-      :run-id="bulkToken"
+      :expected-token-override="bulkProjected?.confirm_token || ''"
       tier="C"
       :projected-counts="bulkProjectedCounts"
       :description="bulkDescription"
@@ -130,7 +130,6 @@ watch(() => sel.order.length, () => {
 const deleting = ref(false)
 const deleteModalOpen = ref(false)
 const bulkProjected = ref(null)
-const bulkToken = ref('')
 
 const bulkProjectedCounts = computed(() => bulkProjected.value
   ? {
@@ -147,24 +146,22 @@ const bulkDescription = computed(
     : '',
 )
 
-async function _computeSha8(ids) {
-  const canon = [...ids].sort((a, b) => a - b).join(',')
-  const buf = new TextEncoder().encode(canon)
-  const hashBuf = await crypto.subtle.digest('SHA-256', buf)
-  const bytes = new Uint8Array(hashBuf)
-  let hex = ''
-  for (let i = 0; i < 4; i++) {
-    hex += bytes[i].toString(16).padStart(2, '0')
-  }
-  return hex
-}
+// The dry-run response hands the canonical Tier-C confirm token back
+// as `confirm_token` (e.g. `delete-images-1a2b3c4d`), passed straight
+// to the modal via `expected-token-override`. We used to compute the
+// hash client-side via `crypto.subtle.digest`, but (1) that's
+// Secure-Context-gated and undefined on plain-HTTP origins
+// (homelab posture), so the click silently threw TypeError and the
+// modal never opened, and (2) the modal's `kind="images-selection"`
+// produced `delete-images-selection-<sha8>` while the backend
+// expected `delete-images-<sha8>` — so it never would have worked
+// even on HTTPS. Operator-flagged 2026-05-27.
 
 async function onDeleteClick() {
   if (!sel.order.length) return
   deleting.value = true
   try {
     bulkProjected.value = await adminStore.projectBulkImageDelete(sel.order)
-    bulkToken.value = await _computeSha8(sel.order)
     deleteModalOpen.value = true
   } finally {
     deleting.value = false