docs: Mintlify CLI, Node LTS note, and config filename clarifications

[Dragboyz]

What changed? Why?

• Switched “Mint CLI” to “Mintlify CLI” and updated commands to npx mintlify dev to match current tooling and reduce contributor confusion.
• Updated Node requirement to “Node.js 18.17+ (LTS recommended). Also tested with Node 20 and 22.”
• Clarified Mintlify config reference to “docs.json or mint.json.”
• Kept contribution guidance consistent (“Preview locally with the Mintlify CLI”).
• Prefer npx to avoid global installs; added note on using the latest CLI via npx mintlify@latest dev (or update global with npm i -g mintlify@latest).

Notes to reviewers

• Scope is README-only; no content structure or code changes.
• No links/badges removed; wording clarified and modernized.
• Confirm whether the repo uses docs.json or mint.json in docs/.

How has it been tested?

• Verified Markdown renders in GitHub preview (headings, lists, code fences).
• Checked badges/links render and resolve.
• Sanity-checked instructions with current Mintlify CLI and Node LTS.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1