fix: reposition transient/popup windows into visible area on focus and demands-attention

[MatrixNeoKozak]

What

Transient/popup windows (dialogs, modals, notifications) are real MetaWindows rejected by add_filter, so they're never in the scrollable clone container and the existing ensureViewport/scroll machinery can't reach them. Two paths were broken:

1. Popup gets focus: focus_handler early-returned for transients without repositioning them, leaving them clamped at the monitor edge.
2. Popup demands attention (focus denied): no window-demands-attention handler existed, so background-spawned popups stayed invisible.

Fix adds a repositionTransient helper that clamps the window's frame rect to its monitor's work area via move_frame, then calls it on both paths:

• From focus_handler before the early return for transients
• From a new window-demands-attention signal handler that repositions attention-demanding popups without stealing focus

Why

This change resolves the target issue or improvement.

How to test

Verify that the project builds/runs correctly and the specific bug/improvement is addressed.

Fixes #1174