zsh completion uninstall strips the user's leading blank lines from .zshrc #2015

What happened

openspec completion uninstall zsh strips every blank line at the top of .zshrc, not just the separator line that completion install zsh added. A .zshrc that starts with blank lines doesn't come back byte for byte after an install/uninstall round trip.

Round trip through ZshInstaller.configureZshrc and then removeZshrcConfig:

The cause is in removeZshrcConfig: after removing the block, while (lines[0].trim() === '') lines.shift() runs regardless of where the block was. It also strips leading blank lines when the user moved the block further down the file.

#1872 fixed the same thing for bash (removeBashrcConfig now drops one separator line, and only when the block was at the top). Its test comment says zsh "already" round-trips byte for byte, but it doesn't for files that start with blank lines.

What you expected instead

Uninstall hands .zshrc back exactly as install found it, the same as bash after #1872. It should drop only the separator line install added, and only when the block sits at the top of the file.

Minimal steps to reproduce

1. printf '\n\nalias ll="ls -la"\n' > ~/.zshrc
2. openspec completion install zsh (standard zsh, not Oh My Zsh)
3. openspec completion uninstall zsh
4. .zshrc now starts with alias ll=...; the two leading blank lines are gone.

OpenSpec version

1.13.2 (main, source checkout)

Coding agent and model

Found and reproduced by Claude Code (Claude Opus 5.5) working for @huiq777; a fix PR follows.