CLI still calls the version-history counter "version" after the UI renamed it "snapshot"

[tylerpotts]

Summary

#515 renamed Nebi's internal version counter to "snapshot" in the UI and in the server-written rollback description ("Rolled back to snapshot N"). The CLI still calls the same counter "version", so a user moving between the UI and the CLI sees two names for one number, and "version" now collides with the pixi.toml version field the UI shows as the primary label.

Places to update

• cmd/nebi/workspace_version.go rollback Long help text: still says the command creates a "Rolled back to version N" snapshot. The store and worker now write "Rolled back to snapshot N", so this text is factually wrong.
• cmd/nebi/workspace_version.go rollback success message: Rolled back %s to version %d (now version %d). Run 'pixi install' to apply.
• cmd/nebi/workspace_version.go list/tag table headers: VERSION\tCREATED\tHASH\tDESCRIPTION and VERSION\tCREATED
• cmd/nebi/workspace.go tags table header: TAG\tVERSION\tCREATED\tUPDATED
• docs/src/content/docs/examples/version-rollback.md sample CLI output block for nebi workspace tags (header TAG VERSION CREATED) once the CLI changes.

Open question

Whether nebi workspace version <subcommand> itself should be renamed or aliased (nebi workspace snapshot). That is a breaking CLI change and probably wants its own discussion; the string fixes above are not breaking.

Context

Follow-up promised in #515 (comment). Related: #508, #78.