bug(plans): Edit scheduled purchase fails with 'Failed to load plan details' (regression after #773/PR #780) #1403

Repro

1. Navigate to Plans page.
2. Find a plan with scheduled (planned) purchases listed under Planned Purchases.
3. Next to a scheduled purchase, click the 'Edit' button.

Expected

The modal to edit the purchase or plan opens (pre-filled with current data).

Actual

Error message: 'Failed to load plan details'. The edit modal does not open.

Context

Issue #773 (edit fails with this message) was closed as fixed by PR #780. This is a regression: the failure has reappeared. The original PR #780 changed the Edit button to pass plan_id instead of the execution's own id; that logic may have been undone or broken by a subsequent change.

Sheet reference

Plans tab, row 6.2.