Fix iTerm2 Settings window detection

[Miyou]

iTerm2 Settings exposes AXFullScreenButton=null, like the hotkey windows ignored since #1813. The broad hotkey heuristic therefore classifies Settings as a popup, so it never reaches dialog handling or focus-follows-mouse.

Exempt AXIdentifier=mainPreferencesWindow from that filter. Its AXDialog subrole then lets the existing dialog heuristic float it, while iTerm hotkey windows remain ignored. Add a sanitized debug-windows dump as regression coverage.

#1813

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