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/api/auth.go

@@ -4,7 +4,7 @@ import (
 	"encoding/json"
 	"net/http"
 
-	"smartrun/backend/internal/garmin"
+	"geniusrun/backend/internal/garmin"
 )
 
 type authResponse struct {