Calendar improvements

[hingobway]

• timeline: show specific guest names in collapsed cabin where appropriate
• overview: add buttons for selecting the next/previous days
• overview: added sorting options for selected day (sort by cabin vs. sort by date)

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

client/src/app/calendar/_components/Overview.tsx:39

• [nitpick] The variable name 'd' is ambiguous. It should be renamed to 'date' or something more descriptive.

let d = selectedDate ?? 0;