fix(scheduled-tasks): prevent dual-server double dispatch of daily tasks (#2713)

* fix(scheduled-tasks): claim schedule occurrences across server instances

Two OpenChamber servers sharing project config each armed timers and both
dispatched the same daily/weekly/cron/once slot (#2710). Claim the occurrence
in shared config under a cross-process write lock before creating a session.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* fix(scheduled-tasks): harden occurrence claim failure and lock ownership

Address PR review blockers: release running-slot bookkeeping when claim
throws, avoid silently dropping an armed occurrence after a due-slack sync,
verify lock-file ownership on release, and cover real on-disk lock behavior.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* fix(scheduled-tasks): always release running slot on state-write failures

Wrap runTask bookkeeping in finally so claim, manual-start, and completion
lock timeouts cannot stuck-run a task; drop the diskNext claim guard that
suppressed later occurrences; recover unparseable locks via mtime age.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* fix(scheduled-tasks): stop re-arming past nextRunAt and clear stuck running

Only schedule future nextRunAt values so once-task losers and claim-failed
paths cannot spin delay-0 retries. Clear past once nextRunAt on claim, and on
completion-write failure retry terminal status so manual runNow still returns
the session instead of a hard 500 with lastStatus stuck running.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* fix(scheduled-tasks): release write chain on lock acquire timeout

withProjectWriteLock left the in-process promise chain pending when
acquireProjectFileLock timed out, wedging every later project write and
stranding runTask before finally. Always release the chain; surface
persistError on run; record once claim failures in task state.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

---------

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/lib/i18n/messages/uk.ts

@@ -237,6 +237,7 @@ export const dict: Record<I18nKey, string> = {
   "sessions.scheduledTasks.dialog.toast.deleted": "Заплановане завдання видалено",
   "sessions.scheduledTasks.dialog.toast.deleteFailed": "Не вдалося видалити завдання",
   "sessions.scheduledTasks.dialog.toast.started": "Завдання розпочато",
+  "sessions.scheduledTasks.dialog.toast.startedPersistWarning": "Завдання запущено, але його стан не вдалося зберегти. Воно може й надалі відображатися як виконуване до наступного успішного запуску.",
   "sessions.scheduledTasks.dialog.toast.runFailed": "Не вдалося виконати завдання",
   "sessions.scheduledTasks.dialog.confirm.deleteTask": "Видалити заплановане завдання \"{taskName}\"?",
   'sessions.scheduledTasks.dialog.confirm.deleteLoopFile': 'Видалити циклічне завдання «{taskName}» і його Markdown-файл?',