I spend most of my day in chat and notes apps and need quick finance math without switching screens. Please build an iOS custom keyboard extension that works like a numpad and adds one‑tap shortcuts for common finance formulas: percentage change, profit margin, and simple compound interest. I should be able to enter values, see a small on‑keyboard preview of the result, and tap Insert to paste the result into the current text field of whatever app I’m using (e.g., messaging or notes). Support decimals and negatives, backspace/clear, basic rounding and percent/currency formatting. Keep it offline (no Full Access), handle cases where third‑party keyboards are disallowed gracefully, and make sure it looks good in light/dark mode on both iPhone and iPad.