feat(abstract-utxo): add comprehensive README and update .gitignore

modules/abstract-utxo/.gitignore

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 node_modules/
 .idea/
 dist/
+.vscode

modules/abstract-utxo/README.md

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 # BitGo abstract-utxo
+
+This module provides the foundational `AbstractUtxoCoin` class and concrete implementations for Bitcoin and Bitcoin-like UTXO-based cryptocurrencies within the BitGo platform.
+
+## Overview
+
+The `AbstractUtxoCoin` class serves as the base implementation for all UTXO-based coins, providing common functionality for transaction building, signing, verification, and recovery operations. Each supported cryptocurrency extends this class to provide coin-specific behavior while leveraging the shared UTXO infrastructure.
+
+## Supported Coins
+
+Concrete implementations are provided in the `src/impl/` directory:
+
+- **btc/** - Bitcoin (BTC) and Bitcoin testnet variants
+- **bch/** - Bitcoin Cash (BCH)
+- **bcha/** - Bitcoin Cash ABC (BCHA)
+- **bsv/** - Bitcoin SV (BSV)
+- **btg/** - Bitcoin Gold (BTG)
+- **ltc/** - Litecoin (LTC)
+- **dash/** - Dash (DASH)
+- **doge/** - Dogecoin (DOGE)
+- **zec/** - Zcash (ZEC)
+
+## Key Features
+
+### Transaction Operations
+- **Building & Signing**: Support for both legacy and PSBT transaction formats
+- **Multi-signature**: 2-of-3 multisig with various script types (P2SH, P2WSH, P2SH-P2WSH, P2TR-MuSig2)
+- **Verification**: Comprehensive transaction intent verification before signing
+- **Explanation**: Decode and explain transaction details (inputs, outputs, fees)
+
+### Wallet Types
+- **Fixed Script Wallets**: Traditional HD wallets with deterministic address generation
+- **Descriptor Wallets**: Modern wallet format using output script descriptors
+- **Distributed Custody**: Support for enterprise custody configurations
+
+### Address Management
+- Address validation and derivation verification
+- Support for multiple address formats (base58, bech32, cashaddr for BCH)
+- Chain/index-based address generation for fixed script wallets
+
+### Recovery Operations
+- **Backup Key Recovery**: Recover funds using backup key when BitGo is unavailable
+- **Cross-Chain Recovery**: Recover coins sent to wrong chain (e.g., BTC sent to LTC address)
+- **V1 Wallet Recovery**: Support for legacy V1 wallet recovery
+
+### Advanced Features
+- BIP322 message signing support
+- MuSig2 for Taproot multisig
+- Replay protection for chain splits
+- Custom change address handling
+- RBF (Replace-by-Fee) transaction support
+
+## Development Setup
+
+### VSCode Configuration
+
+For an optimal development experience in VSCode, configure the Mocha Test Explorer with the following settings in `.vscode/settings.json`:
+
+```json
+{
+  "mochaExplorer.files": "test/**/*.ts",
+  "mochaExplorer.nodeArgv": ["--import", "tsx"],
+  "mochaExplorer.logpanel": true
+}
+```
+
+This configuration enables:
+- **Test Discovery**: Automatically finds all TypeScript test files in the `test/` directory
+- **TypeScript Support**: Uses `tsx` for running TypeScript tests without compilation
+- **Log Panel**: Displays test output for easier debugging
+
+### Running Tests
+
+With the Mocha Test Explorer configured, you can:
+- View and run individual tests or test suites from the VSCode Test Explorer panel
+- Set breakpoints and debug tests directly in the editor
+- Monitor test output in the integrated log panel