Restructure frontend code to allow for extensions (#4721)

# Description of Changes
Move frontend code into `core` folder and add infrastructure for
`proprietary` folder to include premium, non-OSS features

frontend/src/core/components/hotkeys/HotkeyDisplay.tsx

@@ -0,0 +1,58 @@
+import React from 'react';
+import { HotkeyBinding } from '@app/utils/hotkeys';
+import { useHotkeys } from '@app/contexts/HotkeyContext';
+
+interface HotkeyDisplayProps {
+  binding: HotkeyBinding | null | undefined;
+  size?: 'sm' | 'md';
+  muted?: boolean;
+}
+
+const baseKeyStyle: React.CSSProperties = {
+  display: 'inline-flex',
+  alignItems: 'center',
+  justifyContent: 'center',
+  borderRadius: '0.375rem',
+  background: 'var(--mantine-color-gray-1)',
+  border: '1px solid var(--mantine-color-gray-3)',
+  padding: '0.125rem 0.35rem',
+  fontSize: '0.75rem',
+  lineHeight: 1,
+  fontFamily: 'var(--mantine-font-family-monospace, monospace)',
+  minWidth: '1.35rem',
+  color: 'var(--mantine-color-text)',
+};
+
+export const HotkeyDisplay: React.FC<HotkeyDisplayProps> = ({ binding, size = 'sm', muted = false }) => {
+  const { getDisplayParts } = useHotkeys();
+  const parts = getDisplayParts(binding);
+
+  if (!binding || parts.length === 0) {
+    return null;
+  }
+
+  const keyStyle = size === 'md'
+    ? { ...baseKeyStyle, fontSize: '0.85rem', padding: '0.2rem 0.5rem' }
+    : baseKeyStyle;
+
+  return (
+    <span
+      style={{
+        display: 'inline-flex',
+        alignItems: 'center',
+        gap: '0.25rem',
+        color: muted ? 'var(--mantine-color-dimmed)' : 'inherit',
+        fontWeight: muted ? 500 : 600,
+      }}
+    >
+      {parts.map((part, index) => (
+        <React.Fragment key={`${part}-${index}`}>
+          <kbd style={keyStyle}>{part}</kbd>
+          {index < parts.length - 1 && <span aria-hidden style={{ fontWeight: 400 }}>+</span>}
+        </React.Fragment>
+      ))}
+    </span>
+  );
+};
+
+export default HotkeyDisplay;