feat: add auth0-cli skill for CLI resource management

[cristiandouce]

Summary

Adds a new auth0-cli skill to the core auth0 plugin, providing comprehensive guidance for managing Auth0 resources via the CLI. This skill helps AI agents generate correct auth0 CLI commands instead of hallucinating non-existent flags and subcommands.

What's included

New skill: auth0-cli

• SKILL.md — Overview covering installation, authentication (interactive + CI/CD), command categories, common mistakes, and security best practices
• references/commands.md — Complete CLI command reference organized by category (apps, APIs, users, roles, organizations, actions, logs, universal login, testing) with detailed flag tables
• references/workflows.md — Step-by-step workflow recipes for common tasks: setting up new apps, debugging auth failures, bulk user management, deploying actions, log streaming, and CI/CD automation
• references/advanced.md — Advanced features including Terraform generation, attack protection, custom domains, email/phone providers, event streams, token exchange, and network ACLs

Cross-references across all existing skills

Added auth0-cli as a related skill in all 11 existing skills so agents can discover it when working on any Auth0 integration:

• Core skills: auth0-quickstart, auth0-migration, auth0-mfa
• SDK skills: auth0-react, auth0-nextjs, auth0-vue, auth0-angular, auth0-express, auth0-fastify, auth0-fastify-api, auth0-react-native

Plugin and marketplace updates

• Updated plugin.json description to mention CLI management
• Updated marketplace.json description and keywords to include cli
• Updated README.md with the new skill in listings and project structure

Why this matters

Without this skill, AI agents frequently hallucinate incorrect CLI commands — using non-existent flags like auth0 logs list --follow instead of the correct auth0 logs tail, or suggesting environment variables are auto-detected for authentication instead of the actual auth0 login --client-id --client-secret --domain command. During evaluation, the skill improved assertion pass rates from 61% to 100% across test scenarios covering SPA creation, auth debugging, and CI/CD automation.