Release v4.4: keyboard shortcuts are now machine-wide, not per-profile

Fixes issue #14: shortcuts were stored on each Profile, so one set on profile A
didn't apply on profile B and seemed to vanish on switch. They now live in
AppConfig (one set shared by every profile). RemSoundSettingsStore's Load*/Save*
hotkey methods re-point to AppConfig (callers unchanged); the per-profile cache
fields, profile load/save plumbing, and the HotkeySetting helper class are removed.
Profile's HotkeyRecord fields stay only for back-compat deserialization.

On upgrade, shortcuts reset to defaults (there's no single correct set to carry over
since profiles could hold different/partial sets). A one-time startup notice tells
upgraders to re-set them; fresh installs are silently marked done (nothing to reset).

Manual, About changelog and RELEASE_NOTES updated; csproj <Version> 4.4.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

MANUAL.md

@@ -768,6 +768,8 @@ Alt+F4| Close (the standard Windows shortcut)
 
 ## 15. Global hotkeys (work even when minimised)
 
+Your keyboard shortcuts are **shared across all your profiles** — set one once and it works on every profile, and stays put when you switch between them. (Before version 4.4 they were saved separately inside each profile, so a shortcut set on one profile wouldn't work on another. If you're upgrading, your shortcuts will have gone back to their defaults the first time you run the new version — just set the ones you use again, once.)
+
 You set these up in the Keyboard shortcuts dialog (Ctrl+K, or Options → Keyboard shortcuts). The dialog is a single list of every hotkey you can set: **Enter** sets the highlighted row, **Del** clears it (back to _not set_), and **Escape** or the Close button closes the dialog. The defaults:
 
 Hotkey| Action| Default