Refine media server sync notifications

[120318]

Summary

• Suppress scheduler completed events for pure stale media server sync refreshes
• Carry episode metadata through media server sync events and Telegram notifications
• Cover stale suppression and episode range notification rendering with backend tests

Tests

• ./aethera.sh test-backend tests/test_media_server_sync_boundaries.py tests/test_telegram_notification_renderer.py tests/test_message_renderer.py
• ./scripts/review_with_gates.sh

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