feat(timecard-entries): auto-select open timecard based on selected event

[tomas-goncalves]

When creating a timecard entry, the timecard field now automatically filters to only show open timecards that cover the selected event's date.

• If one timecard matches, it collapses to the same display as when there's only one open timecard
• If multiple match, the dropdown is filtered to only the valid options
• If none match (shouldn't happen), an error message is shown mentioning this is weird
• If no timecards are open at all, a message says so instead of hiding the field entirely (improvement)

[DaAwesomeP]

Can we do this all in the template/on page render instead?

[tomas-goncalves]

No - the logic needs to run again when the selected event changes

[NoRePercussions]

I also would prefer to precompute the mapping to keep business logic in the backend.