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.

backend/app/routers/webhooks.py

@@ -0,0 +1,152 @@
+"""
+GitHub Webhooks Router
+
+Receives and processes GitHub webhook events for PR automation.
+Part of Phase Q/Q2 - Merge Queue & Automation Strategy.
+
+Related docs: OPERATOR_PR_EVENT_HANDLERS.md, MERGE_QUEUE_PLAN.md
+"""
+
+from fastapi import APIRouter, Request, HTTPException, Depends, Header
+from sqlalchemy.ext.asyncio import AsyncSession
+import hmac
+import hashlib
+from typing import Optional
+import logging
+
+from ..database import get_db
+from ..services import github_events
+from ..config import settings
+
+router = APIRouter(prefix="/api/webhooks", tags=["Webhooks"])
+
+logger = logging.getLogger(__name__)
+
+
+def verify_github_signature(payload: bytes, signature: str, secret: str) -> bool:
+    """Verify GitHub webhook signature"""
+    if not signature or not signature.startswith("sha256="):
+        return False
+
+    expected_signature = "sha256=" + hmac.new(
+        secret.encode(),
+        payload,
+        hashlib.sha256
+    ).hexdigest()
+
+    return hmac.compare_digest(signature, expected_signature)
+
+
+@router.post("/github")
+async def github_webhook(
+    request: Request,
+    x_hub_signature_256: Optional[str] = Header(None),
+    x_github_event: Optional[str] = Header(None),
+    db: AsyncSession = Depends(get_db)
+):
+    """
+    Receive GitHub webhook events
+
+    This endpoint receives webhook events from GitHub for:
+    - Pull requests (opened, closed, merged, labeled, etc.)
+    - Pull request reviews (submitted, approved, changes_requested)
+    - Status checks (check_run, check_suite completed)
+
+    Events are processed by the github_events service and logged to the database.
+
+    **Security**: Webhooks are verified using HMAC-SHA256 signature.
+
+    **Setup**: In GitHub repository settings → Webhooks:
+    - Payload URL: https://your-domain.com/api/webhooks/github
+    - Content type: application/json
+    - Secret: Set GITHUB_WEBHOOK_SECRET environment variable
+    - Events: Pull requests, Pull request reviews, Statuses, Check runs
+    """
+
+    # Read request body
+    body = await request.body()
+
+    # Verify signature if secret is configured
+    webhook_secret = getattr(settings, 'GITHUB_WEBHOOK_SECRET', None)
+    if webhook_secret and x_hub_signature_256:
+        if not verify_github_signature(body, x_hub_signature_256, webhook_secret):
+            logger.warning("Invalid GitHub webhook signature")
+            raise HTTPException(status_code=401, detail="Invalid signature")
+    elif webhook_secret and not x_hub_signature_256:
+        logger.warning("Missing GitHub webhook signature")
+        raise HTTPException(status_code=401, detail="Missing signature")
+
+    # Verify event type header
+    if not x_github_event:
+        raise HTTPException(status_code=400, detail="Missing X-GitHub-Event header")
+
+    # Parse JSON payload
+    try:
+        payload = await request.json()
+    except Exception as e:
+        logger.error(f"Failed to parse webhook payload: {e}")
+        raise HTTPException(status_code=400, detail="Invalid JSON payload")
+
+    # Log webhook received
+    logger.info(
+        f"GitHub webhook received: {x_github_event} | "
+        f"Action: {payload.get('action')} | "
+        f"PR: #{payload.get('pull_request', {}).get('number', 'N/A')}"
+    )
+
+    # Process event asynchronously
+    try:
+        await github_events.handle_event(
+            event_type=x_github_event,
+            payload=payload,
+            db=db
+        )
+    except Exception as e:
+        logger.error(f"Error processing GitHub event: {e}", exc_info=True)
+        # Return 200 even on processing errors to avoid GitHub retries
+        # Errors are logged for debugging
+        return {"status": "received", "processing_error": str(e)}
+
+    return {
+        "status": "received",
+        "event": x_github_event,
+        "action": payload.get("action"),
+        "pr_number": payload.get("pull_request", {}).get("number")
+    }
+
+
+@router.get("/github/ping")
+async def github_webhook_ping():
+    """
+    Ping endpoint for testing GitHub webhook configuration
+
+    Use this to verify your webhook is reachable before setting it up in GitHub.
+    """
+    return {
+        "status": "ok",
+        "message": "GitHub webhook endpoint is reachable",
+        "configured": hasattr(settings, 'GITHUB_WEBHOOK_SECRET') and settings.GITHUB_WEBHOOK_SECRET is not None
+    }
+
+
+@router.get("/status")
+async def webhooks_status():
+    """
+    Get webhook configuration status
+
+    Returns information about which webhooks are configured and ready.
+    """
+    return {
+        "github": {
+            "endpoint": "/api/webhooks/github",
+            "configured": hasattr(settings, 'GITHUB_WEBHOOK_SECRET') and settings.GITHUB_WEBHOOK_SECRET is not None,
+            "events_supported": [
+                "pull_request",
+                "pull_request_review",
+                "pull_request_review_comment",
+                "status",
+                "check_run",
+                "check_suite"
+            ]
+        }
+    }