docs: add missing flags to cli reference

[ChinmayMhatre]

What

This PR syncs the openui create documentation in cli.mdx with the actual flags supported by the CLI (which are already fully implemented and documented in packages/openui-cli/README.md). Several newer flags regarding template selection, OpenUI Cloud authentication, and installation behavior were missing from the official website documentation.

Changes

• Added missing -t, --template, --api-key, --auth, and --no-install flags to the cli.mdx Options table.
• Expanded the "What it does" section to clarify how the CLI handles template selection.
• Added a "Template-specific .env" section detailing the differences between the openui-chat and openui-cloud setups.
• Updated the example commands to demonstrate scaffolding with specific templates and authentication methods.

Test Plan

Verified that the markdown formatting renders correctly and strictly mirrors the existing, accurate README.md documentation.

• Not applicable (explain why)
• Verified locally

Checklist

• I linked a related issue, if applicable
• I updated docs/README when needed
• I considered backwards compatibility

[ChinmayMhatre]

Resolves #725

[vishxrad]

Good catch! Thanks for this pr.