fix(ui): store coordinates_json in sweep runs for flowfield restore

Sweep runs were storing coordinates_json: null, causing
restoreRunById to bail (geometry_snapshot was always null for
sweep data). Click-to-restore in Plot Builder and Data Explorer
now works for sweep runs.

Made-with: Cursor

Author: aeronauty

flexfoil-ui/src/components/panels/SolvePanel.tsx

@@ -806,7 +806,7 @@ export function SolvePanel() {
             solver_mode: data.solverMode,
             success: data.success,
             error: data.error,
-            coordinates_json: null,
+            coordinates_json: serializePoints(data.panels),
             panels_json: serializePoints(data.panels),
             flaps_json: data.flaps.length > 0 ? JSON.stringify(data.flaps) : null,
           });