Add /opt/rocm/bin to PATH in zshrc when it exists

ROCm installs to /opt/rocm (not /opt/rocm-X.Y versioning). The
upstream /etc/profile.d/rocm.sh tries to add /opt/rocm/bin to PATH
but uses 'append_path' which is a fish-shell function, not a bash/zsh
built-in — so on a zsh login the export is a no-op and the rocm
tools (amd-smi, rocm-smi, rocminfo, hipcc, etc.) are unreachable
without explicit PATH setup.

Add /opt/rocm/bin to the top of the path array in dot_zshrc.tmpl
when the directory exists on the host. Use stat() with the
not-(not-...) bool coercion (pitfall #35 in the chezmoi-bootstrap-
runbook skill) to avoid rendering the stat map's string repr.

Conditional on the directory existing so Pis (no ROCm) don't get a
dead PATH entry. Verified on miche:
  PATH=/usr/bin:/bin:/usr/local/sbin:/usr/local/bin:/usr/bin/site_perl:    /usr/bin/vendor_perl:/usr/bin/core_perl:/opt/rocm/bin
  /opt/rocm/bin/amd-smi
  /opt/rocm/bin/rocm-smi
  /opt/rocm/bin/rocminfo

amd-smi version: AMDSMI Tool: 26.4.0+3309c6114a | ROCm version: 7.13.0

dot_zshrc.tmpl

@@ -90,6 +90,9 @@ export TMUX_PLUGIN_MANAGER_PATH=~/.tmux/plugins/tpm
 # ---------------------------------------------------------------------------
 typeset -U path
 path=(
+    {{- if not (not (stat "/opt/rocm/bin")) }}
+    /opt/rocm/bin                      # ROCm tools first (rocminfo, rocm-smi, amd-smi, hipcc, etc.)
+    {{- end }}
     $HOME/.local/bin
     $HOME/.bin
     $path