Run Prettier across projects

Problem:
Prettier was not running when I saved Emacs buffers.

Why?
- prettier-js-mode needs needs node; lorri exposes node to direnv; direnv
  exposes node to Emacs; lorri was not working as expected.

Solution:
Now that I'm using nix-buffer, I can properly expose node (and other
dependencies) to my Emacs buffers. Now Prettier is working.

Commentary:
Since prettier hadn't worked for so long, I stopped thinking about it. As such,
I did not include it as a dependency in boilerplate/typescript. I added it
now. I retroactively ran prettier across a few of my frontend projects to unify
the code styling.

I may need to run...
```shell
$ cd ~/briefcase
$ nix-shell
$ npx prettier --list-different "**/*.{js,ts,jsx,tsx,html,css,json}"
```
...to see which files I should have formatted.

website/sandbox/contentful/src/store.ts

@@ -22,9 +22,9 @@ export const { actions, reducer } = createSlice({
   name: "application",
   initialState,
   reducers: {
-    toggleIsLoading: state => ({ ...state, isLoading: !state.isLoading }),
-    setBooks: (state, action) => ({ ... state, books: action.payload }),
-  }
+    toggleIsLoading: (state) => ({ ...state, isLoading: !state.isLoading }),
+    setBooks: (state, action) => ({ ...state, books: action.payload }),
+  },
 });
 
 /**