fix(fusion_clock): code-review hardening [19.0.5.0.1]

- _cron_generate: per-rule savepoint isolation (one bad rule can't abort the
  whole daily batch)
- fclk_attach_recurrence: clear an existing recurrence first (no orphaned rule
  generating forever)
- fclk_apply_planner_cell: collapse split rows (search was limit=1 after the
  UNIQUE drop, orphaning extras)
- fclk_release_shift: reject non-posted/open shifts (raw-POST guard)
- delete_open_shift: report success=false when nothing was deleted + JS surfaces it
- _generate: log before removing an empty recurrence
Tests added for collapse, re-attach, draft-release.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

fusion_clock/static/src/js/fusion_clock_shift_planner.js

@@ -428,7 +428,14 @@ export class FusionClockShiftPlanner extends Component {
                 schedule_id: id,
                 week_start: this.state.weekStart,
             });
-            if (!result.error) {
+            if (result.error || result.success === false) {
+                this.notification.add(result.error || result.message || "Could not remove open shift.", {
+                    type: "warning",
+                });
+                if (result.data) {
+                    this._applyData(result.data);
+                }
+            } else {
                 this._applyData(result.data);
             }
         } catch (error) {