Enhancement: mount host SSH keys into container for in-container git workflows

[abitofhelp]

Summary

Mount the host's ~/.ssh directory into the container as a read-only
volume so users can run git operations (clone, fetch, pull, push)
entirely inside the container without switching to the host.

Proposed Change

Add to _dev_container() in .zshrc:

-v "$HOME/.ssh":/home/dev/.ssh:ro

Considerations

• Mount as :ro to protect private keys from accidental modification.
• The container's SSH config IdentityFile paths must match the mount
  point (e.g., /home/dev/.ssh/id_mike_macpro_gh).
• May need known_hosts copied or mounted as well.
• The container user (dev) must have read access to the mounted files
  (UID/GID mapping via entrypoint already handles this).

Motivation

Enables a single-terminal workflow: edit with vim, build, test, and
commit/push entirely inside the container. Currently, git operations
require switching to the host terminal.

[abitofhelp]

Migrated to abitofhelp/dev_containers#1. This repository is deprecated in favor of the monorepo.