Ambient effects across base + story scenes, brighter trigger sparkles, search-spot polish

Ambient effects are data-driven now. Each base location and story scene can declare its atmospheric effects (dust, particles, mist, whatever the scene calls for) in data instead of being hardcoded per scene. Adding atmosphere to a new scene is a data edit, not a code change.

Trigger sparkles got brighter and denser. The sparkle indicator on interactive triggers was easy to miss against busy backgrounds — especially on first play. Density bumped up so the cue reads cleanly even with a lot going on in the scene.

Search-spot triggers skip a redundant image step in their tap flow. The digsite-student NPC moved to a position that fits the scene staging better. Arena herald art assets are in.