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.

tests/test_api_admin.py

@@ -140,6 +140,11 @@ async def test_bulk_delete_dry_run_returns_counts(client, db, tmp_path):
     assert body["images_found"] == 2
     assert body["bytes_on_disk"] == 30
     assert body["missing_ids"] == [9_999_999]
+    # Dry-run hands the canonical Tier-C confirm token back so the
+    # frontend doesn't recompute SHA-256 client-side (crypto.subtle
+    # is Secure-Context-gated; FC runs over plain HTTP).
+    assert body["confirm_token"].startswith("delete-images-")
+    assert len(body["confirm_token"]) == len("delete-images-") + 8
 
 
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