Fix crash from unchecked windowNumber -> CGWindowID conversion

[Leunammih]

Summary

Both ControlItem.windowID and the frame-change handler in IceBarPanel convert
NSWindow.windowNumber to CGWindowID with the non-failable initializer:

CGWindowID(window.windowNumber)

windowNumber is Int, CGWindowID is UInt32, and this initializer traps on
overflow rather than returning nil. On macOS 26, windowNumber can return a value
outside UInt32's range for menu bar item windows (reported in #580 as consistently
greater than UInt32.max), which crashes the app with EXC_BREAKPOINT/SIGTRAP —
matching the stack traces in #977 and other recent crash reports, and one I hit
myself on 0.11.12.

This swaps both call sites to the failable CGWindowID(exactly:), so an
out-of-range value degrades to nil (the existing optional-chaining call sites
already handle that gracefully) instead of crashing the process.

• Ice/MenuBar/ControlItem/ControlItem.swift — windowID getter
• Ice/UI/IceBar/IceBar.swift — the control item's frame-change publisher, used to
  detect when the menu bar is hidden by the system

Testing

• Builds clean (Debug, Xcode 26.6).
• Ran the built app for ~27 hours of normal use with no crash and no new entries in
  ~/Library/Logs/DiagnosticReports/, versus multiple same-day crashes on 0.11.12
  before this change.

Fixes #977. Likely related to #580, #786, #867 (macOS 26 crashes around showing
hidden items / the Ice Bar).

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