[PowerAccent] Fix injection hygiene and reset state on focus loss

[crutkas]

Summary

Fixes PowerAccent injection hygiene and a stuck accent-menu state when the selector loses focus.

What this changes

• Inject arrow keys with the extended-key flag. Replaces SendKeys.SendWait("{LEFT}"/"{RIGHT}") with WindowsFunctions.SendArrowKey(VK_LEFT/VK_RIGHT), which sets KEYEVENTF_EXTENDEDKEY on both the down and up events. Without it the synthesized arrows carry the non-extended scan code and some apps treat them as NumLock-dependent numpad navigation instead of the arrow cluster.
• Tag injected keys so the centralized hook ignores them (dwExtraInfo = 0x110, mirroring CENTRALIZED_KEYBOARD_HOOK_DONT_TRIGGER_FLAG) so PowerAccent's own injections can't re-trigger other shortcuts.
• Reset keyboard state on focus loss. New ForceReset() (added to the KeyboardListener WinRT type/IDL) is wired to the selector's Deactivated event, so the accent menu can't be left stuck if focus is taken mid-selection.
• Make the listener's state flags std::atomic. They are written from the low-level hook thread (OnKeyDown/OnKeyUp) and from the UI/Dispatcher thread (ForceReset). A mutex is intentionally avoided: the OnKeyDown/OnKeyUp callbacks Dispatcher.Invoke onto the UI thread where ForceReset runs, so a lock held across them would deadlock.

Testing

• Builds Release x64 (PowerAccent.Core + PowerAccentKeyboardService) clean against current main. StyleCop passes.

This is one of a small set of related "stuck key" hardening fixes; each stands alone.

[github-actions]

@check-spelling-bot Report

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❌ Errors and Warnings	Count
⚠️ binary-file	1
⚠️ duplicate-pattern	2
❌ forbidden-pattern	1
⚠️ large-file	1

See ❌ Event descriptions for more information.

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