Add an active-only border mode

[qeude]

Summary

• add an optional active_only=on mode that only keeps a border for the focused window
• reuse the active border in active_only mode to reduce churn during focus changes
• improve active_only responsiveness on space changes
• document that inactive_color has no visible effect in active_only mode

Motivation

This adds a lower-memory mode for setups that do not need inactive window borders. The default behavior stays unchanged unless active_only=on is explicitly enabled.

Testing

• make
• manually ran borders active_only=on and verified focus changes and space changes still update the border
• verified the default mode still builds and keeps the existing multi-window behavior

[Bellavene]

Why this overcomplication? Just set inactive to alpha color

[qeude]

@Bellavene because inactive to alpha uses resources still

[YetAnotherDev]

I would love this, I vibe coded a quick replacement that uses about 35mb (appkit) of memory and I have been using it but i assume that JB with this feature it would be even less without the appkit overhead. In its current configuration i have seen JB use over 500MB.

[qeude]

@YetAnotherDev I'm not using JB anymore as I started building my own open source window manager with this feature built-in but as far as I remember:

• JB is actually interfacing this to AppKit under the hood (not 100% sure about this, it's been a while)
• With that fix it was using ~30mb of memory

[Bellavene]

Dunno what you are talking about, my is using 60Mb of RAM right now.