claude-code-plugin: improve dev experience (skills, subagents, structure)

[KennyVaneetvelde]

The Claude Code plugin in this repo was thrown together quickly when marketplaces first came out and could use a proper second pass. Currently it consists of just some skills and subagents to help with development against Atomic Agents.

Goals:

• Audit existing skills/subagents and improve clarity, descriptions, and triggers.
• Add skills for the most common dev workflows (creating a new agent, creating a new tool, creating a choice/orchestrator agent, wiring context providers).
• Better discoverability and docs in the plugin README.
• Examples / templates that match the framework's current best practices.

Open to PRs and suggestions on which workflows would be most valuable to support first.