[FEATURE] Strategy: Supertrend with ATR trailing exits

[sjackson0109]

Implement a Supertrend-based directional strategy with ATR-driven trailing exits.

Dependency:

• Blocked by Strategy Catalogue schema: [FEATURE] Strategy Catalogue definition and schema #121
• Catalogue row and defaults required before merge.

Implementation scope:

• Entry: Supertrend flip with optional trend filter (EMA direction).
• Exit: ATR trailing stop with configurable multiplier and activation rules.
• Include optional pullback entry mode.
• Include long/short toggles and timeframe parameters.
• Integrate slippage/fee-aware backtest path.

Acceptance criteria:

• Strategy registered in catalogue.
• Exits verified in simulation for both long and short paths.
• KPI report and parameter set stored per schema.