Expose some gadget-only callins to replay widgets

There are some callins that are gadget-only, like `ProjectileCreated`. It would be nice if they were exposed to widgets when watching a replay (for headless analysis), or perhaps even for spectators in general.

Start by locating the ProjectileCreated callin and the code that exposes callins to widgets during replay or headless analysis. Compare the existing gadget-only path with widget and spectator handling, then define which callins should be exposed and how replay availability is verified. Done means the selected callins are available to the intended replay consumers without changing unrelated behavior.

Written by the indexing model from the issue text.