feature: Add keyboard shortcuts for comparison form and table search #222

Introduce intuitive keyboard shortcuts across the application to enhance developer ergonomics:

• Press / to focus the search input (in CompareForm or LeaderboardTable).
• Press Ctrl + Enter (or Cmd + Enter) inside CompareForm inputs to submit the comparison.
• Press Escape to clear inputs or reset focus.

Motivation

Developers appreciate thoughtful keyboard ergonomics. Subtle shortcuts give the app a polished, pro-tier feel that earns respect and upvotes on Hacker News and Reddit.

Tasks

• Implement a lightweight keyboard listener hook (e.g., useHotkeys or useEffect on window).
• Add keyboard shortcut visual indicator badges (e.g., <kbd className="border rounded px-1.5 text-xs">⌘↵</kbd>) inside input fields or submit buttons.
• Ensure shortcuts do not trigger when typing inside other inputs or dialogs.
• Verify accessibility and prevent browser shortcut conflicts.

Files to Check

• src/features/comparison/components/compare-form.tsx
• src/features/leaderboard/components/leaderboard-table.tsx
• src/components/ui/input.tsx