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/sync/mapping.go

@@ -5,9 +5,9 @@ import (
 	"strings"
 	"time"
 
-	"smartrun/backend/internal/classify"
-	"smartrun/backend/internal/garmin"
-	"smartrun/backend/internal/store"
+	"geniusrun/backend/internal/classify"
+	"geniusrun/backend/internal/garmin"
+	"geniusrun/backend/internal/store"
 )
 
 // isRunningActivityType reports whether a Garmin activityType.typeKey