fix(health): add root-level /health endpoint for Railway healthcheck

Railway checks /health but all API routes are under /api/v1/.
This adds a lightweight root /health endpoint that returns
{"status": "ok"} — no auth, no DB, no middleware blocking.

This fixes the "1/1 replicas never became healthy" Railway error.

https://claude.ai/code/session_01W1rJthWDkasijTdXCfxVHs

salesflow-saas/backend/app/main.py

@@ -115,6 +115,13 @@ app.add_middleware(
     allow_headers=["*"],
 )
 
+
+@app.get("/health")
+async def root_health():
+    """Root-level health check for Railway/load balancer healthchecks."""
+    return {"status": "ok"}
+
+
 # API Routes
 app.include_router(api_router, prefix="/api/v1")