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>

src/RemSound.App/MainForm.cs

@@ -1380,6 +1380,8 @@ public sealed class MainForm : Form
     /// </summary>
     private void RunStartupNotices()
     {
+        if (IsDisposed) return;
+        MaybeShowKeyboardShortcutsGlobalNotice();
         if (IsDisposed) return;
         MaybeShowWhatsNewAfterUpdate();
         if (IsDisposed) return;
@@ -1431,6 +1433,55 @@ public sealed class MainForm : Form
         }
     }
 
+    /// <summary>One-time notice (v4.4) telling upgraders that keyboard shortcuts have moved from
+    /// per-profile to machine-wide storage (issue #14), so their shortcuts have reset to defaults and
+    /// need re-setting. Shown once to anyone who ran an earlier version; on a brand-new install (which
+    /// has nothing to reset) it's silently marked done and never shown. Must run BEFORE
+    /// <see cref="MaybeShowWhatsNewAfterUpdate"/>, which overwrites the LastWhatsNewVersion we read to
+    /// tell upgraders apart from fresh installs.</summary>
+    private void MaybeShowKeyboardShortcutsGlobalNotice()
+    {
+        if (IsDisposed) return;
+        AppConfig cfg;
+        try { cfg = AppConfig.Load(); }
+        catch { return; }
+        if (cfg.KeyboardShortcutsGlobalNoticeShown) return;
+
+        // A non-empty LastWhatsNewVersion means a previous version has run on this machine — i.e. this
+        // is an upgrade, so there were per-profile shortcuts that have now reset. A fresh install has it
+        // empty (it's set later, by MaybeShowWhatsNewAfterUpdate) and has nothing to reset.
+        var isUpgrade = !string.IsNullOrEmpty(cfg.LastWhatsNewVersion);
+        if (isUpgrade)
+        {
+            logFile.Event("keyboard shortcuts: showing one-time 'now shared across profiles' notice");
+            var page = new TaskDialogPage
+            {
+                Caption = "RemSound",
+                Heading = "Your keyboard shortcuts are now shared across profiles",
+                Text = "Keyboard shortcuts used to be saved separately for each profile, so a shortcut you set on one "
+                     + "profile wouldn't work on another. From this version they're shared across all your profiles "
+                     + "instead — one set for the whole app, which our users have requested.\n\n"
+                     + "Because of this change, your shortcuts have started fresh at their defaults. If you'd set up any "
+                     + "shortcuts of your own, please set them again in Options → Keyboard shortcuts (Ctrl+K). You only "
+                     + "need to do this once — from now on they'll stay put whatever profile you're on.",
+                Icon = TaskDialogIcon.Information,
+                Buttons = { TaskDialogButton.OK },
+                AllowCancel = true,
+            };
+            try { ForegroundDialog.Show(owner => TaskDialog.ShowDialog(owner, page)); }
+            catch (Exception ex) { logFile.Event($"keyboard shortcuts notice failed: {ex.GetType().Name}: {ex.Message}"); }
+        }
+
+        // Mark done either way (shown to upgraders, silently to fresh installs) so it's strictly one-time.
+        try
+        {
+            var fresh = AppConfig.Load();
+            fresh.KeyboardShortcutsGlobalNoticeShown = true;
+            fresh.Save();
+        }
+        catch { /* harmless — at worst the notice shows again next launch */ }
+    }
+
     /// <summary>If the user opted in (<see cref="AppConfig.ShowWhatsNewAfterUpdate"/>) and the
     /// running version changed since the last launch we recorded, open the About box once so
     /// they see what changed in the update just installed. Always records the current version