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/oAIApp.swift

@@ -133,7 +133,7 @@ struct oAIApp: App {
                     .keyboardShortcut("h", modifiers: [.command, .shift])
 
                 Button("In-App Help") { chatViewModel.showHelp = true }
-                    .keyboardShortcut("/", modifiers: .command)
+                    .keyboardShortcut("h", modifiers: [.command, .control])
 
                 Button("Credits") { chatViewModel.showCredits = true }