feat(rules): add at_startup matcher

[iynaix]

Summary

Add a match.at_startup that only applies during the first 60s after starting umbriel.

Motivation

The primary motivation is for opening applications on certain tags on boot. While this can be done by using window rules, the rules are permanent and apply to all future instances of an application as well; e.g. all future browser windows are also stuck on workspace 1.

Well behaving applications can work around this by specifying a custom app_id or title, but many applications do not support this, e.g. chrome does not set an app_id for incognito windows, nemo does not support specifying either an app_id or title.

Type of Change

• Bug fix
• New feature
• Breaking change
• Refactoring
• Build / packaging
• Documentation

Related Issue

Testing

I've added a unittest for a rule that is applied after 60s.

Manual Coverage

• Tested in a nested Umbriel session
• Tested in a native Umbriel session
• Tested with multiple monitors
• Tested with a scaled output
• Tested with native Wayland applications
• Tested with X11 applications through xwayland-satellite
• Tested with the scrolling layout
• Tested with the dwindle layout

Screenshots / Videos

Checklist

• This PR is ready for review, or it is marked as Draft.
• This change fits SCOPE.md, or its scope was agreed in an issue or on Discord first.
• I read and followed the relevant guidance in CONTRIBUTING.md.
• I ran just format, or this PR has no C++ changes.
• I ran the relevant build, test, lint, or verification commands, or explained why they were not run.
• I functionally verified compositor behavior where automated checks are insufficient.
• I self-reviewed the changes.
• I checked for new warnings or errors.
• I updated docs/ and examples/config.toml, or this PR does not change user-facing configuration or behavior.
• I used canonical names for config keys, IPC actions, paths, and identifiers.

Additional Notes

This is pretty much a direct port of the same functionality in niri: https://niri-wm.github.io/niri/Configuration%3A-Window-Rules.html#at-startup.

[ItsLemmy]

Thank you