Rename smartrun to geniusrun throughout the codebase

Updates the Go module path, cmd/smartrund -> cmd/geniusrund, the
smartrun-dev skill, .gitignore, and every reference in docs/CLAUDE.md
to match.

backend/internal/store/migrations/0009_backfill_horizon.sql

@@ -1,5 +1,5 @@
 -- Backfill horizon used to be a startup-time env var
--- (SMARTRUN_BACKFILL_HORIZON_DAYS) with no UI at all -- exactly the kind of
+-- (GENIUSRUN_BACKFILL_HORIZON_DAYS) with no UI at all -- exactly the kind of
 -- "tunable analysis-engine parameter" this profile table exists for.
 -- Default matches the old env var's default (3 years) so existing
 -- deployments keep their current behavior until the user changes it.