add multiple fallback pools

[xyephy]

Adds support for configuring fallback pools with automatic failover, in both the setup wizard and the settings tab.

• "+ Add fallback pool" picker in the wizard
• Editable card list in settings with reorder, remove, Save & Restart
• TCP reachability check on save catches typos before the restart

Closes #45.

[pavlenex]

Quick glance, this PR touches on too many things, making it hard to review. 1300 lines of codes just for adding a simple option to add a fallback pool seems too much. My biggest concern here is that you touched all configuration steps with this as well, so for example now the flow is completely disrupted. For example, now in the setup user can't add custom pool, but it needs to add a fallback pool. I don't know what approach did @GitGab19 have in mind, but this is pretty large scope for a simple feature. On top of that needs rebase and conflict resolving.

[xyephy]

Quick glance, this PR touches on too many things, making it hard to review. 1300 lines of codes just for adding a simple option to add a fallback pool seems too much. My biggest concern here is that you touched all configuration steps with this as well, so for example now the flow is completely disrupted. For example, now in the setup user can't add custom pool, but it needs to add a fallback pool. I don't know what approach did @GitGab19 have in mind, but this is pretty large scope for a simple feature. On top of that needs rebase and conflict resolving.

I'm simplifying, I realised somethings are already implemented. Now doing cleanup.

[xyephy]

I've pushed a simplified version.

[pavlenex]

@xyephy Much better and cleaner direction. Thanks for addressing. I was able to test it and my pool correctly fall back to a secondary pool.

On my first test I encountered the issue where in the setting page I wasn't able to edit or add more fallbacks pool, fallback pools completely disappeared, see video.

Screen.Recording.2026-04-24.at.11.56.50.mov

Also CI is failing. It also doesn't seem I can add more than one fallback pool, earlier you had a way to add and drag drop them which imo was good UX.

[plebhash]

@pavlenex do we want to add casa21 as an official option for fallback?

if yes, also for JD?

asking because currently only MP port 3333 is exposed, I'd have to ask to expose the JDP port as well