Bug: Separate image update checks from automatic container updates

Feature Description

Add a check-only option that continues checking and notifying about image updates without automatically updating the container.

Before Arcane v2.6.0, containers with com.getarcaneapp.arcane.updater=false were still included in bulk image checks. PR #3405 changed this behavior so images used exclusively by opted-out containers are now excluded from bulk and scheduled checks.

Problem It Solves

Some containers require manual review and planning before updating.

Previously, the updater opt-out label prevented automatic updates while still allowing image update monitoring. It now disables both behaviors, removing visibility into available updates unless each image is checked manually.

Proposed Solution

Provide independent controls for update checking and automatic installation, for example: com.getarcaneapp.arcane.update-check=true com.getarcaneapp.arcane.updater=false

Alternatively, provide three states:

• Auto-update
• Check only
• Ignore completely

This would restore the useful pre-v2.6.0 workflow while preserving the ability to exclude intentionally unmonitored containers.

Alternatives Considered

No response

Additional Context

No response

Would you be willing to work on this feature?

• Yes, I'd like to implement this feature
• I could help with parts of this feature
• No, I'm just suggesting the feature