Fix native shortcut modifier matching

[Qwinty]

Closes #569.

Summary

• require exact modifier sets for native modifier+key and modifier-only combo shortcuts
• delay multi-modifier combo activation briefly so Alt+Tab/other key chords can cancel it before callbacks fire
• release active modifier-only shortcuts when they become part of a chord
• make keymonitor tests platform-aware and cover the Windows Alt+Win regression cases

Verification

• npm test -- tests/unit/main/keymonitor.test.ts
• npx eslint src/main/keymonitor.ts tests/unit/main/keymonitor.test.ts
• npx vue-tsc --noEmit --project tsconfig.lint.json
• git diff --check

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