[nemkutya]

Summary

Make split-group lessons occupy the same horizontal position on every day and period. The timetable grid rendered lessons in raw API return order (getForCohort has no ORDER BY, and buildViewModel sorted nothing), so a group could appear in the left sub-column on Monday and the right sub-column on Tuesday. Every timetable view now orders the lessons of a (day × time) cell deterministically by group identifier before rendering, so group 1 is always the first sub-column, group 2 the second, and 3+ groups scale the same way.

No backend change was needed: lessons reference their groups through an array column (lesson.groupsIds), so the position cannot be expressed as a SQL ORDER BY, and the ordering is a presentation concern shared by three frontend views.

Closes #

Changes

Frontend

• Shared split-group definition (components/timetable/helpers.ts): added isWholeClassGroup and getSplitGroups, so the lesson card label, the card group code and the slot ordering can no longer disagree about which group a lesson belongs to. Replaces two near-duplicate filters in lesson-card.tsx and secondary/helpers.ts.
• Shared slot comparator (components/timetable/helpers.ts): added compareLessonsInSlot — trailing group ordinal first (mat1 before mat2, 3+ groups included), then natural localeCompare(..., { numeric: true }) for names without a number, then week type (A before B), then subject, then id as the final tiebreak. Grouped lessons sort before ungrouped ones, so a whole-class lesson never takes group 1's column. Subject is deliberately not part of the group key, so a group keeps its column when a different subject is taught to each group.
• Grid and PDF (components/timetable/helpers.ts): buildViewModel now sorts each cell's lessons with compareLessonsInSlot. The PDF renders the same model, so it inherits the fix.
• Card view (components/timetable/secondary/helpers.ts): removed the local week-then-id comparator and reused compareLessonsInSlot, so the card view and the grid agree.

Verification

• bun run lint
• bun run typecheck
• bun run build — if bundler config, routers, or server entrypoints changed

Notes

• Ordering was checked against mat1/mat2, 11.A angol1/angol2, mixed subjects (DiKu/Mat), three concurrent groups, a whole-class lesson sharing a cell, and A/B-week lessons of the same group.
• Non-numeric group names (Kezdő/Haladó, Fiú/Lány) have no ordinal, so they fall back to natural alphabetical order.
• Known follow-up, not part of this change: the PDF draws a single group-scoped lesson half-width on the left (pdf/document.tsx), so a lone mat2 still lands left.