Fixes #4548 

This is a stylistic breaking change. We previously would make the output
100% regardless of whether it was markdown or not.

Now: we make the output 100% width only for non-markdown. Markdown has
it's own `max-width` set to `65ch` from the [tailwind
typography](https://github.com/tailwindlabs/tailwindcss-typography)
defaults.

This can be unset via custom css in [app
config](https://docs.marimo.io/guides/configuration/theming/), user
config, or project config. To unset this add the css:

```css
.markdown {
  max-width: unset !important;
}
```

------

<img width="1800" alt="image"
src="https://github.com/user-attachments/assets/6c5db7fd-afb9-40cd-88c3-6f5006ef7042"
/>


-------

This is inline with how Observable does it as well (thanks to @manzt for
pointing this out to me ealier this week unrelated to #4548)

---------

Co-authored-by: Akshay Agrawal <akshay@marimo.io>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

## 📝 Summary

Refreshes:
 - BYOE (bring your own editor) page
 - Fileformat tutorial

Introduces:
 - Reusable functions page

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Akshay Agrawal <akshay@marimo.io>

## 📝 Summary


Thanks for stress testing @akshayka !

This:
- **prevents name thrashing**, this is done by prefixing "reusable"
names with a "*", which lets us detect if the last render was to
"reusable" or not. Let me know if this seems like a bit of a hack, but
keeping the name information seemed more useful that just
 - Adjusts some of the help text
 - Adds a link to the docs in #4497

---------

Co-authored-by: Akshay Agrawal <akshay@marimo.io>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

…4569)

## 📝 Summary

These changes ensure that `FileUploadPlugin` displays singularized label
when uploading multiple files is disallowed.

That is: `mo.ui.file(kind="area", multiple=False)` will render with
label "Drag and drop a file here, or click to open file browser" instead
of "Drag and drop files here, or click to open file browser".

## 🔍 Description of Changes

- Extended default label construction logic in
`frontend/src/plugins/impl/FileUploadPlugin.tsx`
- Added dedicated stories for single file inputs via *area* and *button*
variants
- Added E2E test case

## 📋 Checklist

- [x] I have read the [contributor
guidelines](https://github.com/marimo-team/marimo/blob/main/CONTRIBUTING.md).
- [x] I have added tests for the changes made.
- [x] I have run the code and verified that it works as expected.

(#faq-show-code) was attached to the title  of the show code FAQ 

Original title:

## How do I show cell code in the app view?(#faq-show-code)

Original link:
https://docs.marimo.io/faq/#how-do-i-show-cell-code-in-the-app-viewfaq-show-code


![image](https://github.com/user-attachments/assets/8189fac6-3e01-47e2-9773-f2472eddc464)

## 📜 Reviewers

@mscolnick

## 📝 Summary
Flag removal to turn on toplevel definitions.

Just in queue
Deps:
   #4497 -> #4557 -> this

@akshayka OR @mscolnick

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

## 📝 Summary

fastapi example with direct function calls

Speaking of e2e testing, the example refresh threw an error I couldn't
easily seem to replicate through tests, but unsure of how long it's been
there @mscolnick

Minor edits

* explain returned defs
* simplify reusing functions doc

Point to new usage examples on docs.

The previous workflow used an API that doesn't exist on merged pull
requests (`github.event`)

Fix marimo env when node version is not obtainable. Came up in #4581

## 📝 Summary
Stop gap for flaky test

Supersecedes #4588

@akshayka