Add configurable backtest warmup

[luisleo526]

Summary

• add --warmup-bars to fetch and retain user-selected pre-start OHLCV history
• keep indicator/Pine initialization separate from broker execution by forwarding trade_start_time_ms through local Docker, FastAPI, and direct-library runtimes
• report requested and loaded warmup counts, the expanded provider start, and the effective trading boundary
• document the CLI and direct API behavior

Why

The backtest harness previously conflated the data window with the trading window. Filtering output trades after execution could not undo pre-window positions or stateful trade counters, which caused the corpus moderate/weak results. The release runtime already supports suppressing order commands before a boundary; this PR exposes that boundary and lets users choose the preceding warmup length.

User impact

Users can now pass --warmup-bars N. Those bars initialize indicators, higher-timeframe feeds, and Pine state, while order execution remains disabled until --start. The default remains zero for backward compatibility.

Validation

• ruff check src tests
• ruff format --check src tests
• mypy src
• pytest — 86 passed, 2 optional Docker tests skipped
• real pineforge-release:0.1.12 container run confirmed the configured trade_start_ms in runtime provenance