`hype preview` depends on `tree`

[dolanor]

Description

hype preview doesn't work without the tree cli tool.

Steps to Reproduce

1. Install ubuntu 24.04 and Go
2. git clone https://github.com/gopherguides/hype/
3. cd hype
4. go install ./cmd/hype
5. hype preview -theme github -f hype.md

Expected Behavior

I should be able to use the preview

Actual Behavior

$ hype preview -theme github -f hype.md 
hype version dev (commit: none, built: unknown)
$ hype
------
*github.com/gopherguides/hype/cmd/hype/cli.App

Available Commands:
  Command   Description
  -------   -----------
  blog      static blog generator commands (init, build, new)
  export    export the document to a different format (markdown,json,html,etc...)
  marked    outputs for the Marked app (https://marked2app.com/)
  preview   live preview server with file watching and auto-reload
  slides    outputs slide format for presentation
  validate  validate document integrity without full export
  version   print version information

Error: initial build failed: execute error: filepath: /home/dolanor/src/hype/hype.md
document: Hype
execute error: filepath: /home/dolanor/src/hype/hype.md
cmd: $ tree ./docs
exit: -1
cmd error: exec: "tree": executable file not found in $PATH

Environment

• OS: Ubuntu 24.04
• Hype version: hype version dev (commit: none, built: unknown) (actual: v0.8.0 from source)
• Go version: go version go1.25.0 linux/amd64

Hype Document (if applicable)

the hype.md file from the root directory

Error Output

Error: initial build failed: execute error: filepath: /home/dolanor/src/hype/hype.md
document: Hype
execute error: filepath: /home/dolanor/src/hype/hype.md
cmd: $ tree ./docs
exit: -1
cmd error: exec: "tree": executable file not found in $PATH