feat: Add 24h profit/loss calculator modal

[meetdhorajiya]

Issue #92
Adds a new modal component that allows users to calculate
24-hour profit or loss for a given amount and cryptocurrency.

• Includes a searchable dropdown for coin selection
• Supports dark/light themes using CSS variables
• Disables 'Calculate' button for invalid input (<= 0)
• Clears old results when inputs are changed

[vercel]

@meetdhorajiya is attempting to deploy a commit to the venisha-kalola's projects Team on Vercel.

A member of the Team first needs to authorize it.