Add autoenv add=local subcommand

The `add=local` subcommand creates `.local/bin` if it doesn't exit and
then updates the autoenv to add it to `PATH`.

autoenv/_autoenv

@@ -17,6 +17,7 @@ _autoenv() {
         edit:'edit .enter and .exit scripts in current directory'
         deinit:'remove .enter and .exit scripts in current directory'
         reload:'reload the current environment'
+        add=local:'add .local/bin to PATH'
         add=py:'add Python virtualenv to the autoenv'
       )
       _describe -t commands command commands && ret=0 ;;

autoenv/autoenv.zsh

@@ -22,6 +22,7 @@ commands:
         edit        edit .enter and .exit scripts in current directory
         deinit      remove .enter and .exit scripts in current directory
         reload      reload the current environment
+        add=local   add .local/bin to PATH
         add=py      add Python virtualenv to the autoenv"
       ;;
 
@@ -92,6 +93,27 @@ commands:
       _autoenv_enter $PWD
       ;;
 
+    add=local)  # Add .local/bin to PATH
+      if ! [ -f $PWD/.enter ] || ! [ -f $PWD/.exit ]; then
+        echo '.enter or .exit not found'; return 1
+      fi
+      _autoenv_exit $PWD
+      # Create .local/bin if not present
+      if ! [ -d $PWD/.local/bin ]; then
+        mkdir -p $PWD/.local/bin
+      fi
+      # On enter: store PATH and insert .local/bin
+      echo 'OLDPATH=$PATH' >> .enter
+      echo 'PATH=$PWD/.local/bin:$PATH' >> .enter
+      # On exit: reset PATH
+      echo 'PATH=$OLDPATH' >> .exit
+      echo 'unset OLDPATH' >> .exit
+      # Authorize modified autoenv
+      _autoenv_authorized $PWD/.enter yes
+      _autoenv_authorized $PWD/.exit yes
+      _autoenv_enter $PWD
+      ;;
+
     add=py)  # Add Python virtualenv to the sandbox
       if ! [ -f $PWD/.enter ] || ! [ -f $PWD/.exit ]; then
         echo '.enter or .exit not found'; return 1