Let a stuck backup be stopped instead of stranding the stack (0.67.0)

A backup holds the stack lock for up to twelve hours — a large volume
legitimately takes that long — and stops the stack's containers for a
consistent snapshot. One that died without unwinding therefore left the
stack stopped and refusing every start, stop, restart and deploy with
"Stack 'npmplus' is busy: backup in progress", with nothing to click
until the TTL ran out.

Backups and restores now register themselves in stack_job_service while
they run, with their phase and the helper containers they stream
through. Cancelling sets a flag and removes those containers, which is
what actually ends the long read: the backup then unwinds through its
own finally — the half-written archive goes, the containers it stopped
are started again, the lock is released. Checks sit between two files
and two volumes, never inside one. A restore is not cancellable at all;
it is halfway through writing a stack's data back.

POST /api/stacks/{id}/unlock does that and waits for it. A backup lock
with no job behind it is a leftover, so it is released on one click; a
deploy lock takes an explicit force, because compose keeps running past
its request. GET /api/stacks/{id}/lock and the stack detail response say
what holds the stack and since when, and the stack page turns that into
"Stop backup" / "Release lock".

Startup now clears every lock rather than only expired ones: after a
restart nothing of ours is in flight, the same reasoning the leftover
helper containers already follow.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/pages/StackDetail.tsx

@@ -18,6 +18,7 @@ import { ConfirmDialog } from "@/components/ui/ConfirmDialog";
 import { LogViewer } from "@/components/stacks/LogViewer";
 import { ContainerCard } from "@/components/stacks/ContainerCard";
 import { ActionStatusList } from "@/components/stacks/ActionStatusBanner";
+import { StackLockBanner } from "@/components/stacks/StackLockBanner";
 import { AutoUpdatePanel } from "@/components/stacks/AutoUpdatePanel";
 import { SecretsPanel } from "@/components/stacks/SecretsPanel";
 import { GitPanel } from "@/components/stacks/GitPanel";
@@ -43,8 +44,10 @@ export function StackDetail() {
   const { data, isLoading } = useQuery({
     queryKey: ["stack", id],
     queryFn: () => stacksApi.get(id),
-    // Container state arrives over /ws/events; this is the fallback.
-    refetchInterval: 30000,
+    // Container state arrives over /ws/events; this is the fallback. A stack
+    // held by an operation is watched closely instead — the banner's "stop
+    // the backup" has to turn back into the normal page once it worked.
+    refetchInterval: (query) => (query.state.data?.lock ? 3000 : 30000),
   });
 
   if (isLoading || !data) return <Spinner />;
@@ -99,6 +102,8 @@ export function StackDetail() {
         )}
       </div>
 
+      {data.lock && isAdmin && <StackLockBanner stackId={id} lock={data.lock} />}
+
       <ActionStatusList statuses={actions.statuses} onDismiss={actions.dismissStatus} />
 
       {/* Tabs */}