Fix layout-aware shortcut display on non-US keyboards

[sbertix]

Summary

• Introduces a more robust reverse key code lookup (keyCode(forDisplayedKeyEquivalent:)) that scans the active keyboard layout across multiple modifier states (unmodified, shift, option, shift+option) so shortcut labels match what AppKit displays in the menu bar on non-US keyboards (e.g. AZERTY).
• Passes modifier state through to UCKeyTranslate so shifted/optioned characters display correctly in shortcut labels.
• Broadens TIS input source fallback chain (primary, layout, ASCII-capable) for better coverage of non-Latin input methods, and adds diagnostic logging at critical fallback points.
• Adds 5 layout-agnostic tests for the reverse lookup covering nil results, modifier state priority, option layers, and case-insensitive matching.

Test plan

• All 29 AppShortcutOverrideTests pass
• Verify shortcut labels display correctly on AZERTY keyboard
• Verify shortcut labels display correctly on US QWERTY keyboard
• Verify Ghostty unbinds still work for all app shortcuts

Closes #182