feat(api): add assignee filter to project daily events search

[Dobrunia]

Problem

Event search/filter in project overview did not support filtering by assignee.
Users could filter by marks (resolved/starred/ignored), but not by assigned user.

What was changed

• Extended GraphQL schema:
  • EventsFiltersInput now supports assignee: ID
  • project.dailyEventsPortion now accepts assignee: ID
• Updated resolver pipeline:
  • Project.dailyEventsPortion forwards assignee to EventsFactory.findDailyEventsPortion(...)
• Updated Mongo aggregation in EventsFactory.findDailyEventsPortion(...):
  • Added assignee match: event.assignee === <selectedUserId>
  • Kept mark filters (resolved, starred, ignored) isolated from non-mark fields
• Added resolver tests:
  • verifies assignee is passed through to the factory
  • verifies old call path still works when assignee is not provided

Why

This enables server-side filtering by assigned user without loading all events client-side, preserving pagination and query performance.