Add standard Zsh modelines to remaining library files

[ss-o]

Context

A reviewed commit adds the canonical two-line Zsh editor modeline to the only three tracked .zsh files that still lack it:

• lib/zsh/git-process-output.zsh
• lib/zsh/rpm2cpio.zsh
• lib/zsh/single-line.zsh

The change is comment-only and keeps each shebang first. The candidate is one commit atop next and is already signed.

Acceptance criteria

• Preserve the existing shebangs and add the canonical modelines immediately after them.
• Keep the change limited to the three identified files.
• Verify every tracked .zsh file with zsh -n.
• Confirm the existing rpm2cpio diagnostic is unchanged from next.

Suggested tracker fields

• Type: Chore
• Priority: Low
• Effort: Small
• Status: Todo

This issue records recovery of previously local-only completed work discovered during the archive-first workspace cleanup.