feat: add strategy_ids and tag filtering to all applicable MCP tools

- Add _resolve_backtests() helper: filters backtests by strategy_ids and/or tag
- Add _resolve_sids() helper: resolves strategy_ids from strategy_id, strategy_ids, or tag
- Add strategy_ids + tag params to 7 multi-strategy tools:
  list_strategies, rank_strategies, get_full_analysis, get_trading_activity,
  get_correlation_matrix, get_window_coverage, filter_strategies
- Add tag param to 6 time-series tools (already had strategy_ids):
  get_equity_curve, get_drawdown_series, get_monthly_returns,
  get_yearly_returns, get_rolling_sharpe, get_portfolio_snapshots
- 18 of 23 tools now support tag/strategy_ids filtering
- Single-strategy tools (5) and note tools (5) unchanged

Author: MDUYN