feat: v0.2.0 branding, healthz version, SSE dashboard live

Centralize APP_VERSION 0.2.0; /health and /healthz return version;
startup log line; UI title Security Alert Center v.0.2.0;
SSE /api/v1/stream/events for live dashboard counters.

backend/app/api/v1/health.py

@@ -3,12 +3,12 @@ from sqlalchemy import text
 from sqlalchemy.orm import Session
 
 from app.database import get_db
+from app.version import APP_NAME, APP_VERSION
 
 router = APIRouter(tags=["health"])
 
 
-@router.get("/health")
-def health(db: Session = Depends(get_db)) -> dict:
+def build_health_payload(db: Session) -> dict:
     db_status = "ok"
     try:
         db.execute(text("SELECT 1"))
@@ -18,4 +18,17 @@ def health(db: Session = Depends(get_db)) -> dict:
         "status": "ok" if db_status == "ok" else "degraded",
         "database": db_status,
         "service": "security-alert-center",
+        "name": APP_NAME,
+        "version": APP_VERSION,
     }
+
+
+@router.get("/health")
+def health(db: Session = Depends(get_db)) -> dict:
+    return build_health_payload(db)
+
+
+@router.get("/healthz")
+def healthz(db: Session = Depends(get_db)) -> dict:
+    """Kubernetes-style alias; same payload as /health."""
+    return build_health_payload(db)