Borrower: Loan management

[ardier16]

Describe the feature

Description:
Implement borrower flows for repaying loans and canceling pending offers.

Acceptance Criteria:

• Active loans list (from useOffersByBorrowerPubkey filtered by status):
  • Display borrower's active and pending loans
  • Click to open action modals
• Repayment modal:
  • Display loan details:
    • Collateral amount (LBTC) with asset icon
    • Principal amount (USDT)
    • Interest amount (USDT)
    • APR (%)
    • Expiration block height + "Term Left" countdown
    • Current block height (from useBlockHeight)
  • Repay amount input (auto-fills principal + interest, editable)
  • "Repay Loan" button → Build → Sign with Jade → Broadcast
  • Transaction states: pending → success (txid link) → error (retry)
  • Modal closes on success
• Cancel Offer modal:
  • Confirmation dialog: "Are you sure you want to cancel this offer?"
  • Show offer details (collateral, amount, APR)
  • "Confirm Cancel" button → Build → Sign with Jade → Broadcast
  • Transaction states: pending → success → error (retry)
  • Modal closes on success
• Transaction builders called:
  • buildLoanRepaymentTx() — repay loan
  • buildPreLockCancellationTx() — cancel offer
• All tx signing via Jade (Jade wallet integration #24)
• Manual test: Repay and cancel flows work on testnet

Notes:

• Flows match Figma: "Repay Loan Flow" and "Cancel Borrow Offer Flow"
• Show error message if loan expired (can't repay)
• Post-repayment, lender can claim; show success message