Timeline: Restore missing legend component

[yepzdk]

Description

The timeline legend/explanation box that shows the meaning of different status indicators (completed, current, upcoming, note) is missing from below the timeline.

Current behavior

No legend is displayed below the timeline.

Expected behavior

The legend component should be rendered below the timeline, showing the color/status indicators and their meanings.

Related files

• web/themes/custom/hoeringsportal/templates/components/timeline.html.twig
• web/themes/custom/hoeringsportal/templates/components/project-timeline-legend.html.twig
• web/modules/custom/hoeringsportal_project/src/Helper/ProjectHelper.php - needs to pass legend data

Parent issue

Part of #598

[yepzdk]

Fixed by PR #612