fix(h2): add H2 to TREE_SCHEMA_TYPES for correct sidebar structure

H2 uses schemas (PUBLIC) so the sidebar needs the schema layer to
generate correct qualified table names in SQL queries.

src/lib/databaseCapabilities.ts

@@ -117,6 +117,7 @@ export const TREE_SCHEMA_TYPES = new Set<DatabaseType>([
   "gaussdb",
   "jdbc",
   "trino",
+  "h2",
 ]);
 
 export const PG_LIKE_STRUCTURE_TYPES = new Set<DatabaseType>(["postgres", "redshift", "gaussdb"]);