Add persistent storage for the random generator parameters

[braboj]

[braboj]

Out of scope. arc42 §3.3 lists "Persistence, configuration storage, or per-client state" as out of scope — the service is intentionally stateless, with the distribution supplied per request (AD-3). Persisting generator parameters would introduce the server-side state the design deliberately avoids. Closing as out of scope; reopening would require a deliberate scope change (an ADR amending §3.3).