Standardize action button labels

Action button labels are inconsistent across the apps. Align on:

- Load -> Upload
- Save -> Export
- "D" -> needs a clear name

Open question:
- What does the "D" button do, and what should it be renamed to?

Review the action-button labels across the apps and trace the “D” button to its existing behavior. Confirm its purpose, then align Load with Upload and Save with Export and replace “D” with an agreed clear label. Done means the affected app labels are consistent and the ambiguous button has an unambiguous name.

索引モデルが issue の本文から書いたものです。