Add EESSI client container for macOS-26.x

[TopRichard]

No description provided.

[boegel]

@TopRichard Is the container recipe you're adding here at all specific to macOS?

If so, can you point out there? I guess that should be highlighted with a comment.

If not, we should probably rename the recipe to not even mention macOS? (and I would personally go with macOS-26.x, not Tahoe, but that's a tiny detail)

[TopRichard]

@TopRichard Is the container recipe you're adding here at all specific to macOS?

If so, can you point out there? I guess that should be highlighted with a comment.

If not, we should probably rename the recipe to not even mention macOS? (and I would personally go with macOS-26.x, not Tahoe, but that's a tiny detail)

Yes, the recipe uses the macOS user ID and group ID to allow proper bind mounting.

[boegel]

@TopRichard The Dockerfile should be renamed to also use macOS-26.x?

(and maybe macOS-26 is nicer, but now I'm really nitpicking...)

[boegel]

lgtm