Vikunja 2.3.0:1

Vikunja 2.3.0:1 — package polish

No upstream Vikunja change (still 2.3.0). StartOS package refactor only.

What changed

• Bumped @start9labs/start-sdk to 1.5.1.
• Refactored the install task flow: tasksOnInstall + watchSystemSmtp
  removed; watchInitialUser and a consolidated setupPrimaryUrl now handle
  the post-install "Create Your First User" and "Set Primary URL" tasks.
  Reactive SMTP env is resolved in getVikunjaEnv, so no separate watcher is
  needed.
• Added a top-level instructions.md that StartOS surfaces on install.
• Localized input-validation error messages (username, email, attachment size)
  and the Accounts / Other group labels for all five supported locales.
• Marked the 2.3.0 down migration IMPOSSIBLE and dropped unused docsUrls
  from the manifest.

Compatibility

In-place upgrade from 2.3.0:0. Backups and existing data remain compatible —
the volume layout, JWT secret, store schema, and action IDs are unchanged.

Assets

• vikunja_x86_64.s9pk — for x86_64 servers
• vikunja_aarch64.s9pk — for aarch64 servers (e.g. Raspberry Pi 4,
  Apple-silicon-class boards)