fix(fnm): load managed Node from always-on zsh layer

fnm lived in interactive-only ~/.config/zshrc, so ssh/agents/zsh -c
missed fnm-managed node. Source ~/.config/zsh/*.zsh from .zshenv and
install the fragment as zsh/fnm instead.

.zshenv

@@ -18,7 +18,16 @@ if [[ -d "$HOME/.local/bin" ]]; then
   export PATH
 fi
 
-if [[ -f "${XDG_CONFIG_HOME:-$HOME/.config}/zsh/local.zsh" ]]; then
+# Always-on tool fragments (~/.config/zsh/*.zsh). local.zsh is sourced last so it wins.
+ZSH_ALWAYS_ON_DIR="${XDG_CONFIG_HOME:-$HOME/.config}/zsh"
+if [[ -d "$ZSH_ALWAYS_ON_DIR" ]]; then
+  for f in "$ZSH_ALWAYS_ON_DIR"/*.zsh(N); do
+    [[ ${f:t} == local.zsh ]] && continue
+    # shellcheck disable=SC1090
+    . "$f"
+  done
+fi
+if [[ -f "$ZSH_ALWAYS_ON_DIR/local.zsh" ]]; then
   # shellcheck disable=SC1090
-  . "${XDG_CONFIG_HOME:-$HOME/.config}/zsh/local.zsh"
+  . "$ZSH_ALWAYS_ON_DIR/local.zsh"
 fi