[TP-904] basedliner rewards

[KorbinianK]

This pull request adds support for a new activity type called "Basedliner" to the user profile activity history feature. The changes ensure that "Basedliner" events are properly mapped, displayed, and localized throughout the application.

Activity Type and Mapping Updates

• Added BASEDLINER to the ActivityType enum in ActivityHistory.ts, enabling the system to recognize and categorize this new event type.
• Updated the eventToActivityTypeMap in eventToActivityMapper.ts to map the "Basedliner" event string to the new BASEDLINER activity type.

UI and Localization Enhancements

• Modified ActivityHistoryRow.svelte to display a "double-diamond" icon and the localized "Basedliner" label for events of type BASEDLINER.
• Added the "Basedliner" string to the English localization file en.json for correct display in the UI.

Mock Data Improvements

• Inserted a mock "Basedliner" event into the user activity history response in mock-api/user/history/+server.ts to support development and testing.