zshenv: dedupe PATH with typeset -U

zshenv is read by every zsh, so a nested shell prepended the repo's bin
directories a second time. The NAS showed each of them twice after one
`zsh -l -i`. typeset -U keeps the first occurrence, which is also the
ordering this file intends.

common/zsh/zshenv

@@ -29,6 +29,9 @@ export ANDROID_HOME="$HOME/Android/Sdk"
 export LITELLM_BASE="${LITELLM_BASE:-http://127.0.0.1:4000}"
 
 # Repo scripts come first; host-specific ones shadow the shared ones.
+# typeset -U keeps the array unique, so a nested shell re-reading this file
+# prepends nothing a second time. Without it PATH grows on every subshell.
+typeset -U path PATH
 path=(
   "$DOTFILES/hosts/$DOTFILES_HOST/bin"
   "$DOTFILES/common/bin"