test(plans): pin that a normal-length plan name is not truncated in Planned Purchases #1749

Follow-up to #1742 (#1680), from review feedback.

frontend/tests-e2e/plan-name-width.spec.ts checks that a 100-character plan name doesn't make the Planned Purchases table overflow its wrapper. That catches the overflow regression found during review. But the spec also passes on the old code, because the old narrow truncation (cell-truncate--sm) never overflowed either. So nothing pins the actual #1680 fix: a normal-length plan name should now show in full when there's room.

Proposal

Add an assertion at a wide viewport (1920px) that a typical plan name, for example "RDS Full Coverage Purchase" (about 26 characters), is not truncated: the .plan-name-cell element's scrollWidth <= clientWidth. The same check should fail with the old cell-truncate--sm class. Keep the existing no-overflow check for the 100-character case.