fix: issue 15809 Load complete workspace member data in timeline activities

[deval2498]

Previously, timeline activities were using shouldOnlyLoadRelationIdentifiers=true (default), which only loaded id, name, and avatarUrl fields for the workspace member. However, the workspace member object was being returned as undefined, causing the timeline to fall back to displaying 'Twenty' instead of the actual user's name.

This fix explicitly sets shouldOnlyLoadRelationIdentifiers=false to ensure the complete workspace member relation is loaded with all necessary fields. This resolves the issue where workspace member was always undefined in timeline activity display.

Changes:

• Modified useTimelineActivities hook to load full workspace member data
• Added explanatory comment for the configuration choice

Root cause: Performance optimization PR https://github.com/twentyhq/twenty/pull/14991 introduced relation loading restrictions that inadvertently broke workspace member data loading in timeline activities.

Fixes https://github.com/twentyhq/twenty/issues/15809