#538 auto-closed by a partial fix; loop-route highlight still wrong in UIKit #1346

Follow-ups from #1312, which gave loop-route trip stops position-qualified list identifiers.

1. "Closes #538" overstates the scope — consider reopening.

#538 is the general tracking issue ("OBAListView throwing duplicate identifier exceptions tops the crash list") and asks for a rethink of item identification across the list framework. #1312 fixes TripStopViewModel specifically. Real fix, correct fix, but it auto-closed a broader issue.

2. The second new test is vacuous as a regression guard.

List ids stay unique across the whole trip loads trip_details_1_18196913_no_status.json, whose 53 stop times have 53 distinct stop IDs — so Set(ids).count == ids.count passes against the old id: String { stop.id } implementation too. The first test (A stop visited twice gets two distinct list ids) does genuinely cover the fix, so coverage isn't absent; but a fixture with an actually repeated stop would make the second test mean something.

3. Same loop-route bug remains in the UIKit selection paths (pre-existing).

highlightStopInList and isUserDestination both match on bare stop.id, so on a loop route they resolve/highlight the wrong (first) occurrence. The SwiftUI side already solved this with an anchored vehicleIndex search; the UIKit side hasn't. Not touched by #1312, but it's the same class of bug on the same screen.

Minor: docs/duplicate-trip-stop-ids.md ends with a dangling "Tests do not load TripViewController.view." with no surrounding context.