Probe reactive DAL connectivity for diagnostics

Sends a test probe to the Data Access Layer (DAL) using the reactive client and returns a plain-text status string. This is a developer/diagnostic endpoint — it is not a general-purpose platform health check; for Quarkus SmallRye readiness and liveness probes, use /q/health instead. When to use: call only to verify that the API layer can reach the DAL during development, deployment validation, or incident triage. Preconditions: a valid JWT and a tenant-id header are required. The tenant-id header is validated as present by the request interceptor, but its value is not forwarded to the DAL — the endpoint always passes hardcoded values (testOrgId, testUserId) to the downstream health check, so the caller's tenant context has no effect on the probe result. What you get back: a text/plain body. On a successful DAL round-trip the body is "DAL Health (Reactive): <health>". On a downstream DAL error the failure is recovered and the body is "Error calling DAL: <message>", still returned with a 200 status rather than a non-2xx status.