Add AI agent readiness: course sub-commands, docs, PHP 7.4

[flintfromthebasement]

Summary

Makes the LifterLMS CLI ready for AI coding agents (Claude Code, Cursor, Codex) to use as a primary interface for managing LifterLMS sites.

• New commands: wp llms course content <id> (get course structure in one call) and wp llms course enrollments <id> (list enrolled students) — sub-resource endpoints the Restful bridge doesn't auto-discover
• AI agent guide: docs/ai-agents.md with JSON output patterns, chaining workflows, resource relationships, and CLI vs MCP comparison
• README rewrite: Installation, quick start, full command reference, output format docs, remote site usage
• PHP 7.4 minimum: Bumped from 7.3 (EOL since Nov 2021)
• Changelog: Added v0.0.6 entry

The new commands follow the existing trait pattern (see AddOn/ commands) and dispatch internal REST requests via rest_do_request() — same mechanism the Restful bridge uses.

Context

This pairs with the new LifterLMS MCP server for remote AI access. The CLI covers the local/shell use case (Claude Code, Codex running on the server); the MCP covers the remote use case (Claude Desktop, ChatGPT connecting over HTTP). Both cover the same resources.

Test plan

• Verify wp llms course content <id> returns sections + lessons in table and JSON formats
• Verify wp llms course enrollments <id> returns enrolled students with pagination
• Verify --format=json, --format=count, --fields work on both new commands
• Verify existing auto-generated commands (wp llms course list, etc.) still work
• Verify wp llms course --help shows the new subcommands alongside existing ones
• Verify PHP 7.4 minimum doesn't break anything (no 7.3-only syntax used)

🤖 Generated with Claude Code

[brianhogg]

@cursor review