Show ⌘ instead of Ctrl on macOS in UI hints

[false200]

What is this about?

Problem

Hotkeys in main.js use CommandOrControl, but the UI always shows Ctrl+ — wrong on Mac.

Where to look

• index.html — brand tag (~598), composer hint (~641)
• main.js — shortcuts already correct (~141, 152)

Acceptance criteria

• macOS shows ⌘ / "Cmd"; Windows/Linux show Ctrl
• Labels match real shortcuts: Ctrl+`, Shift+C, V, Enter
• README hotkey table updated if needed

Skills needed

Small JS helper + copy changes. Good intro to cross-platform Electron apps.