Add USGS Earthquake Hazards API source

[mbtariq82]

• Integrate USGS real-time earthquake monitoring
• Fetch significant earthquakes (M≥4.0 or tsunami warnings)
• Display as markers on globe/map with magnitude-based sizing
• Add to dashboard layers and signals

Summary

This PR adds the USGS Earthquake Hazards Program API as a new real-time data source to Crucix, providing natural disaster intelligence alongside existing geopolitical, economic, and satellite sources.

Why

Crucix provides comprehensive OSINT coverage but lacked natural disaster intelligence. Earthquakes represent critical signals that can:

Trigger geopolitical responses (humanitarian aid, border tensions)
Correlate with existing signals (radiation monitoring near nuclear sites, conflict zones)
Provide early warning for cascading events in volatile regions
Expand coverage into climate change and environmental monitoring domains
The USGS API fills this gap with reliable, real-time data that's free and doesn't require authentication.

Scope

• Focused bug fix
• Small UX improvement
• New source
• Dashboard change
• Docs/config change

Validation

Commands run:

# Test USGS source standalone
node apis/sources/usgs.mjs

# Test full sweep integration  
node apis/briefing.mjs | findstr USGS

# Test dashboard server
node --trace-warnings server.mjs
netstat -ano | findstr :3117

Manual validation:
✅ USGS source returns structured earthquake data without errors
✅ Full sweep completes with 30 sources (29/30 successful)
✅ Dashboard server starts on port 3117
✅ Earthquake markers appear on globe/map with correct sizing
✅ Layer toggle includes new "Earthquakes" option
✅ No console errors in browser dev tools

Screenshots

Config and Docs

• No new environment variables
• .env.example updated if needed
• README.md updated if behavior changed

Source Additions

If this PR adds a new source, explain:

• why the source improves signal quality
  The USGS source enhances Crucix's intelligence by adding natural disaster awareness, which often intersects with geopolitical events. Earthquakes can destabilize regions, trigger humanitarian crises, or correlate with military/nuclear activities. This provides early warning signals that complement existing conflict, radiation, and satellite monitoring.

• whether it requires an API key
  No API key required - uses public USGS GeoJSON feed.

• how it degrades when the key is missing
  Graceful degradation: If USGS API is down, source returns empty array with "No recent significant earthquake data" signal.

• what changed in apis/briefing.mjs and dashboard/inject.mjs
  briefing.mjs: Added USGS import and runSource call in Tier 3
  inject.mjs: Added earthquake data processing and signal extraction

Checklist

• This PR stays within one bugfix or one feature family
• I kept unrelated changes out of the diff
• I considered security for any mixed-source content rendering
• I tested the changed path locally