Add per-monitor default layout selection via monitor property

[Kaysera]

Description

This PR adds support for per-monitor default layouts by introducing an optional "monitor" property in layout definitions.

When present, the layout is automatically selected as the default for the specified monitor on startup. This allows different monitors to use different default zone layouts without manual selection after login.

Configuration example

{
  "name": "Ultrawide layout",
  "padding": 0,
  "monitor": "DP-1",
  "zones": [
    ...
  ]
}

"monitor" matches the KWin output name

Layouts without this property behave exactly as before

Behavior

On startup, KZones will assign layouts with a matching "monitor" to that output

Monitors without a match fall back to the first defined layout

If multiple layouts match the same monitor, the first one is used

This allows for multi-monitor setups to have separate defaults

Compatibility

Fully backward compatible

No changes required to existing configs

[zjDrummond]

Sounds like a great idea.

[gerritdevriese]

Has anyone been testing this long term?

[geodro]

I think zones should be per display aspect ratio, for example my display is an ultra wide one and supports split screen, so sometimes I have a very wide one 32:9 and sometimes just normal aspect ratio 16:9

happy to jump in to make the required changes, I was thinking of creating a PR

[Kaysera]

Has anyone been testing this long term?

I have been using this since I opened the PR no problem, but I would appreciate more testers just in case

[Kaysera]

I think zones should be per display aspect ratio, for example my display is an ultra wide one and supports split screen, so sometimes I have a very wide one 32:9 and sometimes just normal aspect ratio 16:9

happy to jump in to make the required changes, I was thinking of creating a PR

I have the same setup and it is something I haven't come around to fix it yet. I have the impression that the display identifier is not exactly the same when it is 32:9 and when it is 16:9, so I'll try to make some room to see if I can find a way to discriminate between ratios

[geodro]

I think zones should be per display aspect ratio, for example my display is an ultra wide one and supports split screen, so sometimes I have a very wide one 32:9 and sometimes just normal aspect ratio 16:9
happy to jump in to make the required changes, I was thinking of creating a PR

I have the same setup and it is something I haven't come around to fix it yet. I have the impression that the display identifier is not exactly the same when it is 32:9 and when it is 16:9, so I'll try to make some room to see if I can find a way to discriminate between ratios

check this PR -> #209 maybe we can merge into a single one, this one works for me

[Kaysera]

I think zones should be per display aspect ratio, for example my display is an ultra wide one and supports split screen, so sometimes I have a very wide one 32:9 and sometimes just normal aspect ratio 16:9
happy to jump in to make the required changes, I was thinking of creating a PR

I have the same setup and it is something I haven't come around to fix it yet. I have the impression that the display identifier is not exactly the same when it is 32:9 and when it is 16:9, so I'll try to make some room to see if I can find a way to discriminate between ratios

check this PR -> #209 maybe we can merge into a single one, this one works for me

I'll check it and see if we can combine it