fix: 🐛 only remove qmd files in reference post render to fix md forma…

…tting issues (#1107)

## Description

Removing the entire `reference/` folder post-render is problematic
because the `_sidebar.yml` file in this folder is referenced under
`metadata-files` in `_quarto.yml`. When this file is removed
post-render, it seems to disrupt Quarto's functionality in VS Code,
affecting its visual mode. As a result, formatting (including column
wrapping at length 72) doesn't work as expected.

Changing the post-render process to remove only `qmd` files resolves
this issue, since (as far as I understand) preserving `_sidebar.yml`
ensures that `_quarto.yml` remains valid and maintains an uninterrupted
visual mode.

Please check if this works for you locally by: 

1. Go to this branch 
2. Run `just build-website` (to get the `_sidebar.yml` back) 
3. In an `md` or a `qmd` file, go to visual mode, save it, and go back
to source mode.

Is the formatting still OK after these steps for you as well? 🤞 

Closes #1089 

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## Checklist

- [X] Ran `just run-all`

_quarto.yml

@@ -1,7 +1,7 @@
 project:
   type: seedcase-theme
   pre-render: rm -rf .storage
-  post-render: rm -rf docs/reference
+  post-render: rm -rf docs/reference/*.qmd
   render:
     - "docs/*"
     - "index.qmd"