Add output markdown option

[nicodevs]

In this AI era, many websites offer a Markdown version of their pages using the same URL with a .md extension (like this: https://laravel.com/docs/12.x/ai-sdk.md) to make them easier for LLMs to consume.

This PR adds a collection option to Jigsaw to automatically generate these .md files.

Usage

In config.php:

  'collections' => [
      'posts' => [
          'path' => 'blog/{filename}',
+          'output_markdown' => true,
      ],
  ],

This produces both blog/my-post/index.html (or blog/my-post.html) and blog/my-post.md for each collection item.

output_markdown=true is in fact a shortcut of the longer config options, which are detailed below:

'output_markdown' => ['title_as_h1' => true, 'table_of_contents' => true]

Title as H1

By default, the title of the resource is used as the level-one heading in the generated Markdown. For this resource:

---
title: How to Install Jigsaw
---

Hello! Today...

…the output will be:

# How to Install Jigsaw

Hello! Today...

If the user does not want this behavior, they can opt out by setting:

'output_markdown' => ['title_as_h1' => false],

Table of Contents

Additionally, by default, the body headings are parsed to build a table of contents at the top of the generated Markdown. For example, given the following document:

---
title: Test
---

## Introduction

This is the intro.

## Installation

You can install the Laravel AI SDK via Composer.

The output will be:

# Test

- [Introduction](#introduction)
- [Installation](#installation)

<a name="introduction"></a>
## Introduction

This is the intro.

<a name="installation"></a>
## Installation

You can install the Laravel AI SDK via Composer.

If the user does not want this behavior, they can opt out by setting:

'output_markdown' => ['table_of_contents' => false],

Implementation Details

When output_markdown is enabled, CollectionItemHandler now returns two OutputFile instances to the build output: the original file and a raw Markdown version.

To add the title and the table of contents to the markdown we have a new class, PlainMarkdownBuilder.

No new dependencies are introduced.

Note

Note for reviewers: many of the listed “Files changed” reflect linting-only modifications.

[gcavanunez]

I really like it! Only spot I've been struggling on is whether it should be

'collections' => [
      'posts' => [
          'path' => 'blog/{filename}',
          'extra_output' => ['markdown'],
      ],
  ],

that way if we include automatic TOC enable/disabling can be something like

'collections' => [
      'posts' => [
          'path' => 'blog/{filename}',
          'extra_output' => ['markdown' => [ 'toc' => false ] ],
      ],
  ],

Lots of nesting, so might be best to keep output_markdown and then output_markdown => [ 'toc' => false] but been wondering commit-ing to a flat config could be more painful down the road

and if we decided to also enable it per collection item be something, on a collection's front matter we could - though maybe this something for future exploration

---
...
extra_output:
  - markdown
---

[tonysm]

Nice! Looks good, only left one comment around a deprecated method

[tonysm]

I think setupSource is deprecated, right? We should use createSource instead

[nicodevs]

Yeah, I followed the rest of the codebase. Perhaps we need to change all occurrences of setupSource in another PR, agree?

[nicodevs]

Thanks @gcavanunez and @tonysm!

I've added the title as H1 and table of contents features. I settled on the config shape detailed in the updated PR description. Let me know what you think.

[tonysm]

@nicodevs looks good to me. Nice work on this! 👍🏼