feat(astro): support lessons without parts or chapters

[AriPerkkio]

• Closes Parts of only one lesson #304
• Example without chapters deployed at https://feat-remove-chapters.tutorial-vite-plugin.pages.dev
  

Adds support for defining lessons without chapters or parts.

src/content/tutorial
│
├── meta.md # Tutorial metadata
│
└── lesson-1 # Lesson in root! No part or chapter.
   ├── content.md
   ├── _files
   └── _solution

src/content/tutorial
│
├── meta.md # Tutorial metadata
│
└── part-1
    └── lesson-1 # Lesson in part! No chapter.
        ├── content.md
        ├── _files
        └── _solution

Custom order can be defined using lessons in metadata:

---
type: 'tutorial'
lessons: ['lesson-one', 'lesson-two']
---

---
type: 'part'
lessons: ['lesson-one', 'lesson-two']
---

Mixing structures is not supported and an error is thrown when these are not followed:

• A tutorial can have one-or-many part's or one-or-many lesson's
• A part can have one-or-many chapter's or one-or-many lesson's

In practice:

src/content/tutorial
├── meta.md # Tutorial
├── lesson-1 # Lesson
└── part-1 # Part

> Error: Cannot mix lessons and parts in a tutorial. Either remove the parts or move root level lessons into a part.

src/content/tutorial
├── meta.md # Tutorial
└── part-1 # Part
    ├── lesson-1 # Lesson
    └── chapter-1 # Chapter

> Error: Cannot mix lessons and chapters in a part. Either remove the chapter from 1-part or move the lessons into a chapter.

However you can have multiple part's, where some contain just chapter's and some contain just lesson's:

src/content/tutorial
├── meta.md # Tutorial
│
├── part-1 # Part with lessons
│   └── lesson-1 # Lesson
│
└── part-2 # Part with chapters
    └── chapter-1 # Chapter

tk-mixed-hierarchy.webm

[AriPerkkio]

I've pretty much rewritten this whole component. I tried to re-use the old styling as much as possible but there can be something I've missed. Here's comparison of demo.tutorialkit.dev and this PR:

[AriPerkkio]

Renders to

[AriPerkkio]

I'm planning to create scripts/start.mjs that can be called like node scripts/start.mjs --dev lessons-in-root to reduce these verbose scripts. But that will be added in follow-up PR.

[AriPerkkio]

/pkg-pr-new

⚡️ Your npm packages are published.
@tutorialkit/astro: npm i https://pkg.pr.new/@tutorialkit/astro@431145a
@tutorialkit/react: npm i https://pkg.pr.new/@tutorialkit/react@431145a
@tutorialkit/runtime: npm i https://pkg.pr.new/@tutorialkit/runtime@431145a
@tutorialkit/theme: npm i https://pkg.pr.new/@tutorialkit/theme@431145a
@tutorialkit/types: npm i https://pkg.pr.new/@tutorialkit/types@431145a