feat(scheduled-tasks): add cron syntax support to task editor dialog (#1593)

Adds a 'Cron' schedule type option to the scheduled task editor, allowing
users to create and edit cron-based schedules through the UI.

- Add cron expression input with inline validation (cron-parser)
- Show next 4 upcoming run times as a preview
- Provide clickable example chips (every 5min, hourly, Monday 9am, etc.)
- Preserve cron expressions when editing existing cron tasks
- Add cron.ts utility module for validation and next-run computation
- Add i18n keys across all 8 locale files

Closes #1586

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/package.json

@@ -51,6 +51,7 @@
     "clsx": "^2.1.1",
     "cmdk": "^1.1.1",
     "codemirror-lang-elixir": "^4.0.0",
+    "cron-parser": "^5.5.0",
     "dompurify": "^3.2.7",
     "express": "^5.1.0",
     "fuse.js": "^7.1.0",