Add liquidation risk simulation CLI for Sovryn

[Baliram77]

This PR adds a new risk command group for liquidation stress testing:

• rsk-cli risk simulate --shock : run Sovryn v1 liquidation simulations under price shocks
• rsk-cli risk sandbox --ltv --threshold : compare default vs custom risk parameters
• rsk-cli risk report --format json|table: structured stress-test output (CI/CD friendly)

Implementation details:

• New risk engine under src/services/risk/ (types, data sources, engine, reporting).
• Sovryn v1 positions fetched from the public subgraph, mapped into BorrowPosition and priced via CoinGecko.
• Logging and spinners use the existing logger and spinner utilities with isExternal flag, so the feature is safe to use both in the CLI and MCP server.
• README updated with a “Liquidation Risk (Stress Testing)” section and example usage.

Testing

• npm run build
• node dist/bin/index.js risk simulate --shock 40
• node dist/bin/index.js risk sandbox --ltv 65 --threshold 80
• rsk-cli risk simulate --shock 40 --asset rbtc (if this isin't work run this first npm link)
• node dist/bin/index.js risk report --format json (may occasionally hit CoinGecko 429 rate limits)