[FEAT] Option to keep Window Manager stack bar interactive regardless of current window focus

Is your feature request related to a problem? Please describe.

I'm always frustrated when I have a stack of windows grouped in one tile and I need to switch to another window (or the desktop) for a moment — the stack bar immediately fades out and becomes completely unclickable, because the widget ties both its visibility and its interactability to whether the currently focused window belongs to the tiled tree.

This means that to switch between windows inside a stack using the mouse, I first have to click back into a tiled window just to "wake up" the stack bar, which defeats part of the convenience of having a visible stack bar in the first place.

I tried to work around this purely with CSS (forcing opacity, pointer-events, visibility), but this doesn't work: the interactability is enforced natively via Tauri's setIgnoreCursorEvents, gated by a "data-allow-mouse-events" attribute that the widget re-renders reactively based on window focus. There's no theme or plugin extension point that can override this, since themes only inject CSS and @seelen/window-manager plugins currently only support the Layouts schema.

Describe the solution you'd like

An additional setting alongside the existing stackBarVisibility option ("Always" | "As needed"), something like:

yaml windowManager: stackBar: visibility: "Always" | "AsNeeded" interactableWhenUnfocused: true | false # new

When interactableWhenUnfocused: true, the stack bar would stay clickable (and visible) even if the focused window/desktop is outside the tiled tree — letting users hover/click stacked windows without needing to refocus a tiled window first.

Describe alternatives you've considered

Overriding this via CSS only — not possible, since the blocking happens at the native window level (setIgnoreCursorEvents), not through any CSS property. Building a custom plugin targeting @seelen/window-manager — not currently possible, since the only documented plugin schema for this widget is Layouts, with no extension point for interaction/focus behavior. Manually patching the installed JS bundle — technically possible but unsupported and would break on every update.

Additional context This seems related to the stackBarVisibility setting added in v2.8.1, which currently only controls visibility ("Always" vs "As needed" with 2+ windows), not interactability. Right now "Always" visibility mode can still show a stack bar the user can't interact with if focus is elsewhere, which feels like a small gap in an otherwise well-thought-out setting.