24h and 12h drop down in settings

Implemented and pushed a readable 24-hour / 12-hour dropdown for clock_time_format in Otter Settings. It stores the existing compatible strftime values (%H:%M / %I:%M %p), retains custom formats, and fixes serialization so string-backed dropdowns remain correctly quoted. Commit: otter-settings ea9f4f7. Verified with zig build -Doptimize=ReleaseFast test (163 tests) and zig build -Doptimize=ReleaseFast.