Fix dead Cmd+/ shortcut for In-App Help; rebind to Ctrl+Cmd+H

Cmd+/ was never reaching the "In-App Help" menu item — AppKit
auto-reserves Cmd+/ to open/focus the app's own Help menu (same
mechanism as Cmd+?), silently pre-empting any custom binding on that
combo, exactly like the earlier Cmd+H (Hide Application) conflict.

Verified live with computer-use before landing on Ctrl+Cmd+H:
Option+Cmd+/ has unpredictable menu-glyph rendering and didn't fire;
Option+Cmd+H is macOS's reserved "Hide Others" shortcut (visibly hid
other app windows when tested). Ctrl+Cmd+H showed no OS-level effect
and correctly opens the panel.

HelpView's search bar was already fully implemented and working —
this was purely a matter of the shortcut never reaching it.

oAI/Views/Screens/HelpView.swift

@@ -213,7 +213,7 @@ private let keyboardShortcuts: [(key: String, description: String)] = [
     ("\u{2318}L", "Conversations"),
     ("\u{21E7}\u{2318}S", "Statistics"),
     ("\u{2318},", "Settings"),
-    ("\u{2318}/", "Help"),
+    ("\u{2303}\u{2318}H", "Help"),
 ]
 
 // MARK: - HelpView