feat: Phase LIVE integration - Production automation and deployment fixes

## Railway Deployment Fixes
- Fix railway.toml startCommand (remove incorrect 'cd backend')
- Enhance Dockerfile with security, health checks, and proper user permissions
- Add comprehensive deployment fix documentation (RAILWAY_DEPLOY_FIX.md)

## Phase Q/Q2 Integration
- Add GitHub webhooks router (/api/webhooks/github) for PR automation
- Integrate Prism Console at /prism endpoint
- Add GITHUB_TOKEN and GITHUB_WEBHOOK_SECRET to config
- Update .env.example with webhook secret

## Documentation
- Create comprehensive GitHub setup guide (GITHUB_SETUP_GUIDE.md)
- Document branch protection, merge queue, and webhook configuration
- Include troubleshooting and testing procedures

## Related
- Phase Q: Merge Queue & Automation (PR #78 - merged)
- Phase Q2: PR Action Intelligence (PR #85 - open)
- Phase 2.5: Infrastructure decisions (PR #63 - open)

This brings the automation stack online and stabilizes Railway deployments.

railway.toml

@@ -7,7 +7,7 @@ numReplicas = 1
 sleepApplication = false
 restartPolicyType = "ON_FAILURE"
 restartPolicyMaxRetries = 10
-startCommand = "cd backend && uvicorn app.main:app --host 0.0.0.0 --port $PORT"
+# startCommand is handled by Dockerfile CMD - no need to override
 
 [[services]]
 name = "blackroad-backend"