fix: avoid pointer grab stuck on button press (Wayland)

[KonTy]

Problem

When a button's onclick command opens a window (e.g. a launcher, popup, or overlay) that steals Wayland focus before the button_release_event arrives back at the EWW bar, GTK's internal pointer grab is never released. This causes the entire bar to get "stuck":

• Hover highlighting stops working on all other buttons
• Clicks either do nothing or re-trigger the originally grabbed button
• The user must wiggle the mouse to break free

This affects every EWW user on Hyprland/Wayland whose bar buttons open external windows. The community workaround has been adding sleep 0.1 before commands.

Root Cause

emit_activate() on button_press_event (line 542 of widget_definitions.rs) triggers GTK's built-in Button activation, which includes an implicit pointer grab via GDK seat grab. If the button_release_event is intercepted by another layer-shell surface that opens before the release arrives, the grab is never freed.

As @Rayzeq analyzed in #1022:

1. GTK button grabs the pointer on press
2. The onclick command opens a window that steals focus
3. The release event goes to the new window, not the bar
4. GTK never receives the release → grab never freed → all events redirect to the stuck button

Fix

Replace emit_activate() with manual :active CSS state management (the same pattern eventbox already uses):

• On press: Set StateFlags::ACTIVE for visual feedback (preserves the button animation)
• On release: Clear ACTIVE and run the command (unchanged behavior)
• On grab_broken: Clear ACTIVE as a safety net if the grab is stolen by another surface

This preserves the press/release visual animation while eliminating the pointer grab that causes the stuck state. No user-facing API changes.

Testing

• Compiled and verified on Arch Linux with Hyprland
• The fix is a single-file change (~18 lines added, 5 removed) in widget_definitions.rs
• Bar buttons that launch external windows (launchers, notification centers, calendar overlays) no longer cause the stuck state

Fixes #1008
Fixes #1022