fix(pres_mgmt): add group as leading sort prefix for event_presentation

Group should partition before priority in the sort chain, consistent with
how all other AE objects are sorted (group → priority → sort → ...).
Was accidentally omitted when switching to build_tmp_sort.

Full order: group → priority DESC → sort ASC → start_datetime ASC → code ASC → name ASC

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/ae_events/ae_events__event_presentation.ts

@@ -685,6 +685,7 @@ export async function process_ae_obj__event_presentation_props({
             // Override generic tmp_sort_* with presentation-specific encoding via
             // build_tmp_sort. Order: priority DESC → sort ASC → start_datetime ASC → code ASC → name ASC
             const { tmp_sort_1, tmp_sort_2 } = build_tmp_sort({
+                prefix: [obj.group ?? '0'],
                 priority: obj.priority,
                 sort: obj.sort,
                 fields_1: [obj.start_datetime, obj.code],