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.

link-dotfiles

@@ -10,11 +10,41 @@
 #
 # Windows / PowerShell: run ./link-dotfiles.ps1 instead (stow has no native
 # Windows port; the .ps1 mirrors this with junctions + symlinks).
+#
+# `--check`: report drift and change nothing. Two kinds are caught. (1) A tracked
+# file whose live copy is no longer a link into this repo: stow would refuse to
+# stow over it, so the repo copy has silently gone stale. `sed -i` and any other
+# write-temp-then-rename editor does this, and so can an app that rewrites its
+# own config atomically. (2) A link into this repo whose target has been removed.
+# Exits 1 on drift.
 set -euo pipefail
 
 repo="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 cd "$repo"
 
+if [ "${1:-}" = "--check" ]; then
+  command -v stow >/dev/null 2>&1 || { echo "error: GNU stow not installed; run ./link-dotfiles once first." >&2; exit 2; }
+  drift=0
+  for spec in "home_root:$HOME" "home_config:$HOME/.config"; do
+    pkg="${spec%%:*}"; target="${spec#*:}"
+    out="$(stow -n -v --target="$target" "$pkg" 2>&1 | grep -v 'simulation mode' || true)"
+    if [ -n "$out" ]; then
+      drift=1
+      echo "✗ $pkg -> $target is not fully linked:"
+      printf '%s\n' "$out" | sed 's/^/    /'
+    fi
+  done
+  dangling="$(find "$HOME" "$HOME/.config" "$HOME/.claude" "$HOME/.claude/bin" "$HOME/.claude/skills" "$HOME/.local/bin" \
+    -maxdepth 1 -xtype l -lname "*dotfiles/*" 2>/dev/null || true)"
+  if [ -n "$dangling" ]; then
+    drift=1
+    echo "✗ links into dotfiles whose target is gone:"
+    printf '%s\n' "$dangling" | sed 's/^/    /'
+  fi
+  [ "$drift" -eq 0 ] && echo "✓ no drift: every tracked file is linked, and no dotfiles link dangles."
+  exit "$drift"
+fi
+
 # `--apps`: install all host CLI tools first, then link. Without it, this only
 # links (fast + idempotent). App install is delegated to the host-aware
 # lk-installers/install-apps.