With several strategies the header cards showed only the first one. Expose
day_pnl and drawdown_pct per strategy and add aggregateStatus() (frontend) so the
cards show the whole account: summed cash/equity/P&L/trades/positions, worst
drawdown, and any halt. Single-strategy runs are unchanged. Adds tests.
Adds MultiStrategyManager: it runs several strategies concurrently, each with
its own TradingEngine seeded with starting_balance * allocation, so one
strategy's losses cannot eat into another's capital. Weights are normalised
across the run ([1,3] -> 25%/75%). Risk limits stay per strategy (each engine
owns a RiskManager).
New API: POST /api/bot/start-many and GET /api/bot/status. The existing
single-strategy endpoints delegate to the manager, so their behaviour is
unchanged. Adds manager tests (allocation, isolation, duplicate keys) and API
tests.
matitos