feat: improve borrow/repay discoverability on positions page

[starksama]

User Feedback

Borrow and repay actions are too hidden in the current positions page UI. Users are having trouble finding them.

Requested Improvements

1. Make Borrow & Repay More Prominent

• Currently these actions are buried — they should be much more visible and accessible from the positions view
• Consider adding prominent action buttons directly on position cards/rows

2. Repay UX — Show Current Balance

• When repaying, display the user's current borrow balance clearly
• Show outstanding debt amount so users know exactly what they owe

3. Target LTV Input for Borrowing

• Add an input for desired LTV (Loan-to-Value ratio)
• Automatically calculate and display the corresponding borrow amount
• This gives users an intuitive way to manage their risk level
• Example: User has $10,000 collateral, sets target LTV to 50% → system shows they can borrow $5,000

Context

This came from direct user feedback. The goal is to make position management (especially borrowing and repaying) more intuitive and less hidden in the UI.

Acceptance Criteria

• Borrow and repay buttons are easily discoverable on the positions page
• Repay modal shows current borrow balance
• Borrow modal includes a target LTV input that calculates the ideal borrow amount #338
• LTV calculation accounts for oracle price, LLTV, and current position state