Agent Plugins 0.4.0

feat: what the second adopter could not do from the front door

A second adopter reported on 2026-09-02, in the announcement thread of the
protocol repository's 0.14.0 release, that they set the plugins up, could not
get a consistent plan for a CRUD feature whose new entity relates to an
existing one, and fell back to a third-party plugin for spec, plan and
implementation. Their two asks were a multi-perspective pass over a plan and
straight-to-the-point instructions with a golden-path example. An independent
review of that plugin against this stack ranked the fixes; this release is the
plugin rows of that ranking, filed as epic:second-adopter-feedback and five
stories in this repository's new planning store.

• One copy-paste install block on the install page and the README, with the
  precondition that the aep binary is on PATH.
• A golden-path page: one recorded run from feature idea to critiqued plan on
  a repository that already exists, every CLI block produced by running it.
• The decomposer enumerates and classifies the epic's domain relations before
  drafting a story; an undecided one becomes a decision-blocker, not a story.
• A plan-time critic panel: four read-only critics, verdicts as immutable
  review-result artifacts, revisions bounded at two rounds; the plugin
  validator now requires the critics and their rubric.
• A domain-first guardrail in the planning skill and a widened ess-schema
  trigger, with the minimal ess/1 document that ess validate accepts.
• The planning store itself, pinned to the aep protocol tree at 0.41.0.
• The one remaining authored protocol spelling in the planning skill is now
  aep.

Every plugin manifest, skill version line and the install pin move to 0.4.0.
Gate: task check, task site-build, claude plugin validate --strict on the
changed plugins, all exit 0.