v0.6.1

Fixes

• Loads real student group memberships from GET /groups?filter[student]=....
• Keeps subject groups such as 5Eth1c and 5TC2c separated correctly per child.
• Uses concrete dated substitution-plan lessons for normal lessons, substitutions, room changes and cancellations.
• Corrects replacement teacher and room selection against the regular weekly plan.
• Adds focused timetable diagnostics.