chore: add Greek translation for empty state (M2-8129)

[farmerpaul]

📝 Description

🔗 Jira Ticket M2-8129

Adds the Greek text for the "no activities" empty state.

📸 Screenshots

🪤 Peer Testing

1. Create an applet for which all activities are not assigned (auto-assign is off, no manual assignments).
2. Open the mobile app, set the language to Greek in user settings, refresh the list of applets, and open the applet.
   Expected outcome: Empty state should show in Greek.