fix: preserve group field in manifest during cmd_edit

The ManifestEntry was being written with group: None instead of
preserving the entry's existing group value during edits.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/idfoto-cli/src/main.rs

@@ -681,7 +681,7 @@ fn cmd_edit(query: String) -> Result<()> {
             name: name.clone(),
             url,
             username,
-            group: None,
+            group: updated_entry.group,
             updated_at: now,
         },
     );