Add helper for formatting buy quantity input with bounds

[TheDEV111]

Closes #400.

Summary of Changes:

• Centralized Bounds: Added BUY_QUANTITY_BOUNDS constant to src/constants/fees.ts (min: 1, max: 100).
• Clamping Helper: Created clampBuyQuantity in src/utils/buyQuantity.ts to robustly clamp inputs and handle float rounding (since keys are discrete whole assets).
• TradeDialog Integration: Hooked clampBuyQuantity into the onBlur event of the trade quantity input in src/components/common/TradeDialog.tsx.
• User Alerts: Rendered an adjustment/warning note under the input to clearly show when clamping or rounding was applied. The note is cleared immediately as soon as the user changes the input value (onChange).
• Full Test Coverage:
  • Wrote comprehensive unit tests in src/utils/__tests__/buyQuantity.test.ts (7/7 passing).
  • Wrote integration tests in src/components/common/__tests__/TradeDialog.buyQuantity.test.tsx (5/5 passing).

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