Add Composables UI docs CLI commands

[alexstyl]

Summary

• add composables docs list, docs search, and docs get
• fetch Composables UI docs from composables.com with a configurable base URL for local testing
• return resolved markdown for docs get and keep JSON for discovery commands

Verification

• ./gradlew :cli:test
• ./gradlew :cli:installDist
• smoke tested docs list, docs search, and docs get against http://localhost:3000