devShells: make all shells inherit from default shell

Currently, important tools from the default shell are lost as soon as select-shell is used to switch to another shell. select-shell itself, for example is missing, which makes it impossible to switch back to another shell.

docs/nix/flake-module.nix

@@ -74,9 +74,12 @@
     {
       devShells.docs = pkgs.callPackage ./shell.nix {
         inherit (self'.packages) docs clan-cli-docs;
-        inherit module-docs;
-        inherit asciinema-player-js;
-        inherit asciinema-player-css;
+        inherit
+          asciinema-player-js
+          asciinema-player-css
+          module-docs
+          self'
+          ;
       };
       packages = {
         docs = pkgs.python3.pkgs.callPackage ./default.nix {

docs/nix/shell.nix

@@ -7,10 +7,14 @@
   asciinema-player-css,
   roboto,
   fira-code,
+  self',
   ...
 }:
 pkgs.mkShell {
-  inputsFrom = [ docs ];
+  inputsFrom = [
+    docs
+    self'.devShells.default
+  ];
   shellHook = ''
     mkdir -p ./site/reference/cli
     cp -af ${module-docs}/* ./site/reference/