[UX] Add keyboard shortcut hints to toolbar buttons

[adamghaleb]

Description

Keyboard shortcuts are only discoverable via the shortcuts dialog. Toolbar buttons don't show their associated shortcut anywhere.

Expected Behavior

Show shortcut hints on toolbar buttons, e.g.:

• Split button shows "(S)"
• Play button shows "(Space)"
• Delete button shows "(Delete)"

Could be implemented as:

• Suffix in tooltip: "Split at playhead (S)"
• Small <kbd> badge on button hover
• In context menu items

Files

• apps/web/src/components/editor/panels/timeline/timeline-toolbar.tsx
• apps/web/src/components/editor/dialogs/shortcuts-dialog.tsx