refactor(taskbar): refactor taskbar layout with flex and button

[enklht]

Summary

This PR rewrites taskbar implementation to use ui::flex, ui::button to reduce manually computed positionings.

Motivation

The manual layout math made it hard to reason about the placement.
I believe making proper use of flex layout makes the codebase more maintainable, verifiable.

Type of Change

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

Related Issue

none

Testing

• Confirmed that just build, just build release, and just test all pass successfully.
• Verified the taskbar layout across multiple option combinations, focusing on configuration settings that impact layout positioning (group_by_workspace, show_workspace_label, and workspace_label_positioning).
  Testing was primarily on a horizontal bar, with additional validation on a vertical bar.

Manual Coverage

• Tested on Niri
• Tested on Hyprland
• Tested on Sway
• Tested on another compositor:
• Tested with different bar positions and density settings
• Tested at different interface scaling values
• Tested with multiple monitors

Screenshots / Videos

screenshots on horizontal bars:

without workspace grouping:

without workspace labels:

workspace labels at corners:

workspace labels at center:

workspace labels inside the pill:

Checklist

• This PR is ready for review, or it is marked as Draft.
• I read and followed the relevant guidance in CONTRIBUTING.md.
• I ran just format with clang-format v22+ installed, or this PR has no code changes.
• I ran the relevant build or test commands, or explained why they were not run.
• I self-reviewed the changes.
• I checked for new warnings or errors.
• I will update end-user documentation after merge, or this PR does not change user-facing configuration or behavior.
• I added or updated assets/translations/en.json, or this PR adds no new user-facing strings.
• I did not edit non-English translation files unless this PR is explicitly for translation tooling, an import/export sync, or a maintainer-requested locale change.
• I used the existing canonical names for config keys, IPC names, paths, and identifiers.

Additional Notes

[Ly-sec]

Hey @enklht I just tested your PR and it seems like there are some miscalculations uappening.

It seems like the badges can get clipped, there were a few reasons why we had this random math in place, mostly to keep the badges properly positioned :).

[enklht]

Thanks @Ly-sec for checking! I've converted this to a draft PR.
Do you have any idea how I could reproduce the bug you encountered?

[enklht]

Hi @Ly-sec, I adjusted the padding dimension so badges wont get clipped.
Could you give it another try and let me know if it fixes the issue on your end?

[Ly-sec]

Hey @enklht sorry for the late response, I was quite busy :). Would you mind resolving the conflicts? Afterwards I'll gladly merge it.

[enklht]

Thanks @Ly-sec for the review!
I've resolved the merge conflict and added one small follow-up commit to respect the m_minimal flag introduced in the previous PR.

[Ly-sec]

Thank you very much, I'll merge it :).