feat: detect stalled stack updates and add in-app recovery actions (#1347)

* feat: detect stalled stack updates and add in-app recovery actions

Add a backend idle-output backstop that stops a deploy/update compose step
that has gone silent (SENCHO_COMPOSE_STALL_TIMEOUT_MS, default 10m), so a
hung image pull surfaces a fast failure instead of spinning indefinitely.

Surface failed, timed-out, and stalled operations with recovery actions on
the stack page: a desktop chip plus popover menu and an inline mobile card
offering retry, restart, roll back (when a backup exists), refresh state,
and copy diagnostics, all gated by deploy permission. The streaming
deploy/update progress modal is now on by default and warns when output
goes quiet. Container state is refreshed after a failed or stalled
operation, and the UI never sits in an indefinite spinner.

* fix: harden rollback against policy-blocked file mutation and refine recovery

Address review findings on the stalled-update recovery work:

- The rollback route restored backup files before running the policy gate, so
  a policy-blocked rollback could leave the on-disk config rolled back while the
  deployed containers were unchanged. Snapshot the current files first and
  revert them when the gate blocks; if that revert itself fails, escalate it on
  the persistent alert feed since the 409 is already sent.
- Refresh container state after a successful manual rollback (rollback
  redeploys), without mis-recording a refetch failure as a rollback failure.
- Suppress the stalled-output warning once live progress is unavailable.

* test: mock snapshotStackFiles in the atomic-deploy rollback route tests

The rollback route now snapshots stack files before restoring a backup, so its
FileSystemService mock needs snapshotStackFiles. Without it the mocked call
threw and the route returned 500, failing the success-path rollback assertions.

frontend/src/components/settings/AppearanceSection.tsx

@@ -188,7 +188,7 @@ export function AppearanceSection() {
 
                 <SettingsField
                     label="Deploy progress modal"
-                    helper="Stream live output for deploy, restart, update, install, and Git operations."
+                    helper="Stream live output for deploy, restart, update, install, and Git operations, with a warning when an operation goes quiet. On by default; turn it off to run operations without the panel."
                 >
                     <div className="flex items-center gap-2">
                         <Checkbox