Saving a group changes only the fields sent

[edwh]

Split out of #917, which is now only about the postcode.

Summary

• Before: saving a group through the API overwrote every field with whatever the request sent, and blanked any field it didn't send. Sending just a phone number wiped the group's name, location, map position, description, website, timezone, email and network data.
• This hit the Archive action. Archiving re-sent the whole group from the browser, and that saved the network data as the text "[object Object]".
• After: saving a group changes only the fields the request sends. Changing the location still updates the map position and country to match.
• Archiving now sends only the archive date.
• Timezones: when a group's timezone changes, its future events are moved to the new timezone. Before, a request that didn't mention the timezone counted as changing it to nothing. Now only a request that actually sends a different timezone moves the events.

Code Quality Review

• The change is in updateGroupv2. Admin- and coordinator-only fields (area, postcode, archive date) follow the same rule: they're only updated when sent.
• The edit form still sends every field, so editing a group works as before.

Test Plan

• PHPUnit: a host updating just the phone number leaves every other field, and future events' timezone, unchanged.
• PHPUnit: archiving with only the date keeps the group's name and network data.
• Jest: the Archive action sends only the group id and archive date.
• CI

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud