Keyboard support and UI polish ⌨️
- Added global keyboard support, including numpad, number row and operator symbols
- Added parentheses, square root and power operators
- Improved keypad and history sidebar UI
- Auto-focus the input field on launch and when the app regains focus
- Fixed theme detection on Flatpak
- Fixed button colors and unfocused numpad/shifted symbols
- Added Czech, Hungarian, Ukrainian and French translations
