feat: fold in the portable Claude Code, zsh and git config; add a drift check

Added (all now linked from their live locations):
- home_root/.claude/settings.json. The statusLine command now uses $HOME
  instead of a Linux-only absolute path.
- home_root/.claude/bin/ratecheck and home_root/.claude/skills/australis-design.
- home_config/zsh/claude-config-dir.zsh and home_root/.local/bin/claude-config-dir-init,
  the per-repo Claude Code login helper and its seeding script.
- home_root/.gitconfig and home_config/git/ignore.
- home_root/.zshenv, with the cargo env line guarded so boxes without rust start clean.

link-dotfiles --check reports drift without changing anything: tracked files whose
live copy is no longer a link (stow dry-run conflicts) and links into this repo
that dangle. Exits 1 on drift. Verified against a clean baseline and two planted
drifts, a detached .nanorc and a dangling link.

.mailmap maps every earlier identity to Vuong Hoang: the repo-local 'Your Name'
placeholder config (now removed), host-generated emails, and aider suffixes.

CLAUDE.md: the symlink warning now lists every linked file and points at --check.
README: documents what is and isn't tracked under .claude, the edit rule, and --check.

home_root/.claude/CLAUDE.md

@@ -12,8 +12,11 @@ use `sed -i` or any other write-temp-then-rename tool on
 `~/.claude/CLAUDE.md`:** that replaces the link with a detached copy,
 and the dotfiles backup silently goes stale. It happened once already,
 around 2026-09-18, and went unnoticed until 2026-09-24. The same
-applies to `statusline-command.sh`, `CONTEXT.md` and
-`keybindings.json` in `~/.claude`.
+applies to every other linked file: in `~/.claude` that is
+`settings.json`, `statusline-command.sh`, `CONTEXT.md`,
+`keybindings.json`, `bin/ratecheck` and `skills/australis-design`, plus
+`~/.zshrc`, `~/.zshenv` and `~/.gitconfig`. `~/dotfiles/link-dotfiles
+--check` reports any file that has come loose, and any dangling link.
 
 ## Operator identity