feat: order metadata, consistency/stability metrics, dashboard & MCP improvements

[MDUYN]

Changes

Order Metadata

• Add metadata_json column to Order model with reason tracking
• Tag orders with reasons: buy_signal, sell_signal, scale_out, stop_loss, take_profit
• 43 tests across 7 test files

Consistency & Stability Metrics

• CV-based consistency (scale-invariant) and normalized-std stability metrics
• 8 new fields in BacktestSummaryMetrics
• Weights added to all 4 BacktestEvaluationFocus presets

Dashboard Improvements

• Consistency/Stability KPI cards and ranking table columns
• Absolute-threshold color coding on metrics with best-value stars
• Reason column in orders table, Stop Loss/Take Profit in trades table
• Fixed empty timeline chart (custom canvas 2D rendering)
• Symbol dropdown for timeline filtering
• Fixed report.show(browser=True)

MCP Server

• Consistency/Stability columns in list_strategies
• Added to compare_strategies and rank/filter tool hints
• 32 new MCP server tests

Housekeeping

• Flake8 lint fixes (E501, E128)
• Tutorial notebook and strategy example updates