fix: propagate os.UserHomeDir() errors in snapshot save and load

snapshot save and load were silently ignoring the error from
os.UserHomeDir(), passing an empty home path to ParseSource/ParseDestination
when the home directory cannot be resolved. snapshot remove in the same
file already handles this correctly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018kck6rhh1V315WZq943yoZ

Author: claude

cmd/snapshot.go

@@ -209,7 +209,10 @@ func runSnapshotLoad(cfg *env.Env, tel *telemetry.Client, logger log.Logger) fun
 			return err
 		}
 
-		home, _ := os.UserHomeDir()
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return err
+		}
 		src, err := snapshot.ParseSource(args[0], home)
 		if err != nil {
 			return err
@@ -419,7 +422,10 @@ func runSnapshotSave(cfg *env.Env) func(*cobra.Command, []string) error {
 			destArg = args[0]
 		}
 
-		home, _ := os.UserHomeDir()
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return err
+		}
 		dest, err := snapshot.ParseDestination(destArg, home, time.Now())
 		if err != nil {
 			return err