OnAir v0.1.1 — audit hardening

Floxum audit hardening (→ ≥95). Translator constructor-injection in StreamResource (no resolve()), discussionId set-guard now checks the discussion is visible to the actor, ProviderManager translator DI, service-provider boot(Dispatcher) instead of the event() global, and the stream-end failure now surfaces via app.alerts. Verified booting on a live Flarum 2 install.