Plugins and readable worktree setup

Plugins attach skills, MCP servers and a secret to a repo’s runs. Worktree setup becomes a committed list of named steps, with live progress on the run page.

Added

Plugins are managed from a new Plugins page, ship with a built-in design plugin, and report readiness before a run relies on them
Worktree setup is described as named steps in a committed file, and the run page shows live progress for each step
trau worktree init drafts the setup from what it detects, and the wizard and Worktrees → Setup page edit it
Everything trau writes ends with a footprint line naming its version, so loop-written work is easy to spot

Changed

Setup commands and lane apps run under the PHP version the repo’s Herd site is pinned to

Fixed

Claude Code’s folder-trust dialog no longer stalls unattended runs, and IPv6-only lane apps pass the readiness probe