Proof-of-concept for queuing multiple actions on keybindings

[arkonger]

Summary

Added support for queuing multiple actions on a keybinding by setting the keybinding's action to an array of strings.

Motivation

This is just a proof-of-concept I threw together and will definitely need more testing before merging, but I think it would be quite helpful. As I've configured my keybindings, I've found that I've often had to spawn bash -c to pass several commands through umbriel msg, which makes me think that something like this would be useful not just for myself but for others as well. I thought it was worth submitting to see if this is a feature the team is interested in before I put more effort into testing.

Type of Change

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

Testing

I've only done minimal testing so far, by setting "Mod+Slash" = { action = ["workspace-next", "spawn:kitty"], repeat = false } and then testing in a nested session.

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

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 initialized and updated the SceneFX submodule where required.
• 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.