frontend: Live-sync editor with server updates and add merge option

[kahirokunn]

Summary

This PR improves the resource YAML editor behavior when the underlying resource changes on the server. If the user hasn’t typed anything yet, the editor auto-updates to the latest YAML. If the user has started editing, the editor won’t overwrite changes and instead shows an accessible warning with actions to reload or merge changes.

Related Issue

Fixes #XXXX

Changes

• Updated EditButton/EditorDialog so the editor follows live server updates when not dirty.
• Added a warning banner when the server-side resource changes during editing.
• Added a 3-way merge option with conflict detection and safe fallbacks.

Steps to Test

1. Open any resource details page and click Edit.
2. Without editing, update the same resource elsewhere and confirm the editor auto-updates.
3. Edit at least one character in the editor, then update the resource elsewhere again and confirm:
   • A warning banner appears.
   • Reload from server replaces the editor contents with the latest server version.
   • Merge my changes applies your edits onto the latest server version when there are no conflicts; otherwise you get a conflict message and no automatic overwrite happens.

Screenshots

Notes for the Reviewer

• Merge ignores status, metadata.managedFields, and metadata.resourceVersion to reduce noisy conflicts.

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[kahirokunn]

@joaquimrocha The code has a bit too many lines, but I think this is the ideal editor from a user experience perspective. What do you think?
The reason is that there weren't any good 3-way merge libraries in JavaScript.

My idea is that if the server-side YAML changes, it will eventually cause an optimistic lock error. Therefore, I think it would be a better experience to reflect the server-side YAML to some extent automatically in the editor.

[joaquimrocha]

I think this is likely too complex for us to have it in time for this week's release, but let's try for the next one (and review it as soon as we can).

[kahirokunn]

I think the source code might have even more room for improvement, but I believe the PR and the video effectively convey what we're aiming to achieve.

Please let me join in on this challenge together! 💪

[sniok]

fiy there's also a somewhat related PR that we should make sure it'll work nicely together #4098