Auto-register skills from plugin, simplify OpenCode install

[obra]

Summary

• Plugin config hook injects the skills directory into OpenCode's live config singleton at startup, so skills are discovered automatically — no symlinks or skills.paths config needed
• Installation is now one line in opencode.json: "plugin": ["superpowers@git+https://github.com/obra/superpowers.git"]
• Rewrote install docs (docs/README.opencode.md and .opencode/INSTALL.md), removing ~200 lines of platform-specific symlink instructions
• Added migration notes for users who installed the old symlink-based way
• Added package.json so OpenCode can install superpowers as an npm package from git

How it works

OpenCode's Config.get() returns a cached singleton. Plugins load during bootstrap (Plugin.init()), before skills are lazily discovered. The plugin's config hook pushes its skills directory into config.skills.paths in-memory — when skills are later accessed, they see the modified config and discover all superpowers skills.

Before (old install)

git clone https://github.com/obra/superpowers.git ~/.config/opencode/superpowers
mkdir -p ~/.config/opencode/plugins ~/.config/opencode/skills
ln -s ~/.config/opencode/superpowers/.opencode/plugins/superpowers.js ~/.config/opencode/plugins/superpowers.js
ln -s ~/.config/opencode/superpowers/skills ~/.config/opencode/skills/superpowers
# Plus Windows-specific instructions for Command Prompt, PowerShell, Git Bash...

After (new install)

{
  "plugin": ["superpowers@git+https://github.com/obra/superpowers.git"]
}

Test plan

• Tested with OpenCode — all 14 skills discovered via config hook
• Verified from a clean directory (no local project skills) — plugin loaded from npm cache, skills registered
• Bootstrap context injection still works
• Test on Windows
• Test version pinning with #v5.x.x tag

🤖 Generated with Claude Code