[FEATURE] Strategy: Bollinger mean reversion with regime filter

[sjackson0109]

Implement Bollinger mean-reversion strategy gated by regime filter to avoid trending traps.

Dependency:

• Blocked by Strategy Catalogue schema: [FEATURE] Strategy Catalogue definition and schema #121

Implementation scope:

• Entry: band extension/re-entry rules (configurable z-score / percent-b logic).
• Regime gating: only trade when trend-strength is below threshold (e.g., ADX or BB-width profile).
• Exit: mid-band/target reversion plus protective stop.
• Optional cooldown between re-entries.
• Backtest templates for ranging vs trending subsets.

Acceptance criteria:

• Strategy registered in catalogue with explicit regime assumptions.
• Unit/backtest checks demonstrate reduced trend-regime false entries.
• Paper-mode runnable.