fix(queue): close #1818 — Resume after failure clears the gate

Single failure on a printer with require_previous_success queue items
  permanently skipped every downstream + every new item — the
  _check_previous_success lookback always walked back to the original
  failed row (skipped is excluded from the lookback), and no code path
  could dismiss that failure.

  Three pieces:

  1. PrintQueueItem.gate_acknowledged Boolean column (default False).
     SQLite/Postgres-safe ALTER, dialect-branched DEFAULT.

  2. _check_previous_success skips rows where gate_acknowledged=True so
     acknowledged failures walk past the lookback. Fresh post-resume
     failures still gate independently.

  3. POST /api/v1/queue/printer/{printer_id}/resume — gated on
     QUEUE_UPDATE_ALL — acknowledges failed/aborted items for that
     printer AND restores items where
     status='skipped' AND error_message='Previous print failed or was
     aborted' back to pending in one transaction. Returns
     {acknowledged, restored}.

  Frontend banner above the active Queue tab surfaces blocked printers,
  fires a warning-variant ConfirmModal, and shows a precise toast on
  success.

frontend/src/api/client.ts

@@ -4771,6 +4771,17 @@ export const api = {
     const qs = opts?.skipFilamentCheck ? '?skip_filament_check=true' : '';
     return request<PrintQueueItem>(`/queue/${id}/start${qs}`, { method: 'POST' });
   },
+  /**
+   * Clear the `require_previous_success` gate for a printer after the user
+   * resolves the failure. Acknowledges any failed/aborted predecessors and
+   * restores skipped items whose error_message matches the gate string
+   * back to pending. Returns counts so the UI can render a precise toast.
+   */
+  resumeQueueAfterFailure: (printerId: number) =>
+    request<{ acknowledged: number; restored: number }>(
+      `/queue/printer/${printerId}/resume`,
+      { method: 'POST' },
+    ),
   bulkUpdateQueue: (data: PrintQueueBulkUpdate) =>
     request<PrintQueueBulkUpdateResponse>('/queue/bulk', {
       method: 'PATCH',