feat: minimal sweep WIF QR-code implementation

[psychemist]

Description

This PR adds the ability to sweep funds from an external WIF private key into the user's wallet by scanning a QR code or copy-pasting the raw WIF string.

What This Does

• Scan a QR code containing a WIF private key (or type/paste it manually)
• App derives all standard address types (wpkh, pkh, tr, sh-wpkh) from the key, scans each for funds, and sweeps any balance into the user's wallet
• Supports mainnet (K/L/5) and testnet (c/9) WIF formats
• Accepts raw WIF, wif: prefix, and bitcoin:?wif= URI formats

Flow

• Send screen → "Sweep WIF" button → QR scanner dialog
• Scanned value parsed by WifParser.extract() and validated
• SendViewModel dispatches TransactionType.SWEEP on IO thread
• Wallet.sweep() iterates over descriptors, fully scans each via Esplora, and drains any with balance (confirmed + unconfirmed)
• Success/error toast via existing broadcastResult state flow

Testing

1. Unit tests (JVM, no device needed)
   ./gradlew :app:testDebugUnitTest

2. Install on device/emulator
   ./gradlew installDebug

3. Manual: send testnet4 coins to the wpkh address derived from a test WIF then sweep. Check in-app logs for balance details per descriptor.
   Check out test sweep transaction on testnet4 here:

Screenshots