fish: conf.d/setup: Drop fnm and switch to pnpm

Drop fnm and switch to pnpm for installing npm packages as well as
managing node versions.

Not using npm i -g has the added nicety of not having a node_modules
in /usr/lib.

fish/.config/fish/conf.d/setup.fish

@@ -23,8 +23,9 @@ function __fish_setup_on_tty_login --description "Set up environment on tty logi
         end
     end
 
-    if type -qf fnm
-        fnm env --shell=fish --log-level=quiet | source
+    if test -d {$HOME}/.local/share/pnpm
+        set -gx PNPM_HOME {$HOME}/.local/share/pnpm
+        set -gxp PATH {$HOME}/.local/share/pnpm
     end
 
     # Temporary directory for GStreamer dot files