Establish CLI / Repl best practices based on clig.dev recommendations

[carldebilly]

We should define and document best practices for Repl Toolkit, using clig.dev as a reference and inspiration. This would help standardize how we approach command-line UX and structure within the toolkit, benefiting both contributors and users.

What:

• Research and summarize key recommendations from clig.dev
• Adapt the most relevant guidelines to our context
• Document these best practices clearly within the repo (e.g., in a dedicated markdown file)
• Reference clig.dev appropriately throughout

Why:

• Promote consistency and high quality in command-line interface implementation
• Make it easier for newcomers to contribute and for users to understand and extend Repl Toolkit

References:

• https://clig.dev/