Fix imported_from_german_feeds for central codeweek.de events

[bernardhanna]

Summary

• /api/events/germany sets imported_from_german_feeds via Event::imported().
• That helper only matched legacy city Code Week 4 All codes (bonn, hamburg, …).
• Central export events use source_ref like codeweek-de:{uid} and often cw-codeweek-de, so they were returned as false.
• Datenfreunde then treated them as EU-originated and re-queued them for approval.

Also treat as imported when:

• source_ref starts with codeweek-de:
• mass_added_for is API codeweek_de
• Code Week 4 All code contains codeweek-de

Test plan

• php artisan test --filter=it_should_return_german_events
• After deploy: /api/events/germany?year=2026 for events 1518065 / 1518017 shows imported_from_german_feeds: true

Made with Cursor