Clarify repository menu labels for init vs existing repos

[signalwerk]

This PR updates the “Add Repository” menu labels to make the difference between initializing a new Borg repository and adding an existing one clearer.

The current labels are:

• “New Repository…”
• “Existing Repository…”

I changed them to more explicit Borg-style wording so users can better distinguish between:

• initializing a new/empty repository
• adding or using a repository that already exists

Motivation and Context

I ran into this problem myself. I had an existing Borg repository on my server and wanted to add it to Vorta. I interpreted “New Repository…” as meaning “new to Vorta,” not “initialize a new Borg repository.”

Because of that misunderstanding, I chose the wrong action and initialized a repository where I actually wanted to add an existing one. This destroyed the existing repository state I expected to keep.

Status of this PR

• ⚠️ I do not fully understand Vorta’s translation system yet. I would appreciate help from a maintainer or contributor to make sure this change is completed correctly for all translations.