Fix: Initial Leaderboard filter params

[GODrums]

Motivation

Closes #107.

Description

We now use the current week as default whenever there are no query params. This should have been part of the original PR #105, but I must have missed it.
It also fixes the Dayjs package version, which got merged with a ^ in #92.

Checklist

General

• PR title is clear and descriptive
• PR description explains the purpose and changes
• Code follows project coding standards
• Changes have been tested locally
• Self-review of the code has been done
• Screenshots have been attached (if applicable)
• Documentation has been updated (if applicable)

Client (if applicable)

• UI changes look good on all screen sizes and browsers
• No console errors or warnings
• User experience and accessibility have been tested
• Added Storybook stories for new components
• Components follow design system guidelines (if applicable)

[FelixTJDietrich]

LGTM