Add niri-taskbar widget for vibepanel

[Minimalon]

This commit adds a taskbar widget that displays all open windows on the monitor, similar to niri-taskbar for Waybar.

Features:

• Display all open windows as clickable buttons
• Show app icons and window titles
• Highlight focused window
• Click to focus window
• Filter windows by output/monitor
• Configurable max number of windows

New files:

• src/services/window_list.rs: Service for window list monitoring
• src/widgets/niri_taskbar.rs: Taskbar widget implementation

Modified files:

• src/services/compositor/types.rs: Add Window and WindowListSnapshot types
• src/services/compositor/niri.rs: Implement list_windows() and focus_window()
• src/services/compositor/manager.rs: Add window list methods
• src/services.rs: Add window_list module
• src/styles.rs: Add niri-taskbar CSS classes
• src/widgets/mod.rs: Register niri_taskbar widget

Usage in config.toml:
[[widgets]]
name = niri_taskbar
type = niri_taskbar

[widgets.niri_taskbar]
show_titles = true
show_icons = true
max_windows = 10
filter_by_output = true

[prankstr]

Thank you for the contribution! There is a couple of things I'd like to sort out before being comfortable with bringing this into the codebase though.

First of all, the WindowListService polls for windows every second, this seems unnecessary and could easily be event driven with a callback that would trigger the window fetching on changes instead. Similar to how the WindowTitleService works.

Secondly, the widget is called niri-taskbar but the getting the window list is abstracted behind compositorManager and I know for sure that at least Hyprland could implement list_windows() as well so I think it would make more sense to name the widget just taskbar even if we just support Niri initially.

Lastly, I'd like the config options to be singular instead of plural, i.e show_icon instead of show_icons. I get the reasoning but for consistency I think singular is better. And show_title should probably be false by default instead of true? I feel like most taskbar are icons only by default.

Let me know if you want assistance with any of this.

[Minimalon]

Add new commit

[prankstr]

Thanks :) I went ahead and pushed two commits on top of yours.

The first one fixes a few things that were bugging me. Window ordering is now deterministic, buttons are sorted by workspace index, then layout position, then window ID so they match niri's visual order, same as niri-taskbar. I also fixed so icons reorder live when you move windows around and there's now basic hover/active CSS for the buttons.

The second commit adds icon_size and show_active as config options. icon_size defaults to the theme's pixmap_icon_size and scales with bar size. show_active lets you turn off the focused window highlight if you don't want it.

[prankstr]

Pushed one more commit on top that addresses remaining rough edges:

• Optional workspace and output separators
• Fixed a bug where is_focused wasn't cleared on other windows when a new window gets focus
• max_windows now swaps the focused window into the last visible slot so it's never cut off
• Window list callback now also fires on workspace changes

I'm happy with where this is at now and will merge it. Thanks again for the contribution!