Show total weight difference in weight overview (issue #2133 from backend)

[samir-saidi]

Proposed Changes

• Added totalChange field to processWeight function that calculates cumulative weight change from the first recorded weight entry
• Added "Total Change" column to the weight table showing weight difference since the first measurement
• Updated unit tests to cover the new totalChange calculation logic
• Added translation key totalChange for the new column header

Related Issue(s)

Closes #2133

Please check that the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)

[samir-saidi]

Ready for review now, I have verified that it works on the frontend and the tests pass on my end :) This is my first PR, if there is more information needed (e.g. implementation etc.) please let me know!

I noticed that I accidentally committed package-lock.json, hence there is an extra commit to revert it to the current version of the base branch.