fix(routing/posts): updated slug to match all subdirs

[hamzab-01]

What kind of changes does this PR include?

• Changes with larger consequences (logic, library updates, etc.)

Description

• currently, content/posts are only matched on the first level
• updated slug to match file paths of any depth, for better organisation and flexibility

content/
├─ posts/
│  ├─ 2024/
│  │  ├─ third-post.md
│  │  ├─ fourth-post/
│  │  │  ├─ index.md
│  │  │  ├─ picture.png
│  ├─ 2023/
│  │  ├─ second-post.md
│  ├─ archive/
│  │  ├─ first-post.md
│  ├─ drafts/
│  │  ├─ fifth-post.md

• useful for i18n, can filter by language Feature Request: support i18n #42

content/
├─ posts/
│  ├─ en/
│  │  ├─ example.md
│  ├─ de/
│  │  ├─ example.md
│  ├─ fr/
│  │  ├─ example.md

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[chrismwilliams]

Thanks @hamzab-01 for doing this, and the descrption!