feat: Add check_news tool for economic calendar / news events

[teslashibe]

Summary

Add a check_news tool to query economic calendar events and market-moving news. This enables strategies to avoid trading during high-impact events (FOMC, CPI, etc.).

Motivation

The backtesting agent generates strategies that say "Avoid trading during major news events" but has no tool to actually check for this. This creates a gap between strategy logic and execution capability.

Proposed Interface

// NewsProvider provides access to economic calendar / news events.
type NewsProvider interface {
    // GetEventsInRange returns events between start and end times.
    // Used for backtesting to check historical events during a candle.
    GetEventsInRange(ctx context.Context, asset string, start, end time.Time) ([]NewsEvent, error)
    
    // GetUpcomingEvents returns events within the next N hours.
    // Used for live trading to check before entering positions.
    GetUpcomingEvents(ctx context.Context, asset string, hoursAhead int) ([]NewsEvent, error)
}

// NewsEvent represents a market-moving event.
type NewsEvent struct {
    Time        time.Time
    Title       string
    Impact      string  // "high", "medium", "low"
    Asset       string  // "BTC", "ETH", "*" for macro
    Category    string  // "fed", "cpi", "fomc", "halving", etc.
    Description string
}

Files to Create/Modify

File	Purpose
core/interfaces.go	Add NewsProvider interface
core/types.go	Add NewsEvent type
context.go	Add optional NewsProvider to Context
tools/check_news.go	New check_news tool
tools/registry.go	Register the new tool

Tool Output Example

{
  "asset": "BTC",
  "start_time": "2025-12-20T00:00:00Z",
  "end_time": "2025-12-31T00:00:00Z",
  "events_count": 2,
  "high_impact_events": [
    {
      "time": "2025-12-27T14:00:00Z",
      "title": "FOMC Meeting Minutes",
      "impact": "high",
      "category": "fed"
    }
  ],
  "recommendation": "⚠️ Avoid opening new positions 2 hours before/after high-impact events"
}

Implementation Notes

• Provider-based design allows different implementations (DB, API, mock)
• Optional dependency - tool returns warning if no provider configured
• Works for both backtesting (historical) and live trading (upcoming)

Labels

enhancement, tools