feat(hyperliquid): add leverage, margin, liquidation, and PnL prisms with tests

[helmutkocksmann]

Changes

Adds missing perpetual trading features for the Hyperliquid integration (issue #82):

New Prisms

• HyperliquidSetLeveragePrism — Set leverage (1-50x) with cross/isolated margin support and vault address option
• HyperliquidMarginManagementPrism — Add or remove margin from isolated positions
• HyperliquidLiquidationMonitorPrism — Monitor liquidation proximity with configurable warning (20%) and critical (10%) thresholds, per-position risk levels (safe/warning/critical), and summary counts
• HyperliquidPnLTrackerPrism — Track unrealized PnL, margin utilization, and portfolio ROI across all positions

New Beam

• PositionManagementBeam — Orchestrates liquidation monitoring and PnL tracking, returning overall risk status (healthy/warning/critical)

New Tests (10 test suites)

All Hyperliquid prisms previously had zero test coverage. This PR adds:

• Unit tests for all 6 existing prisms (execute_order, cancel_order, open_orders, token_info, user_state, risk_assessment)
• Unit tests for all 4 new prisms (set_leverage, margin_management, liquidation_monitor, pnl_tracker)
• Liquidation monitor tests include pure-function risk classification and distance-to-liquidation calculation tests
• Integration test for the full trading workflow

Documentation

• Livebook guide (hyperliquid_perps.livemd) covering all prisms, beams, configuration, usage examples, and risk management best practices

Acceptance Criteria Coverage

• Order placement and management (existing prisms)
• Position tracking system (user_state + PnL tracker)
• Risk management implementation (risk_assessment + liquidation_monitor)
• Liquidation monitoring (liquidation_monitor with configurable thresholds)
• Margin management system (margin_management prism)
• Documentation and examples (livebook guide)
• Integration tests for trading operations
• Risk control verification (schema tests + classification tests)

Closes #82