docs: add ADR workflow and update skills

- Add docs/adr/README.md with ADR format, rules, and index
- Add ADR-0001: IMAP thread resolution via In-Reply-To + References
- Add Documentation Rules section to AGENT.md
- Update validate-issue skill: flag ADR-requiring changes
- Rename do-task → implement-task for clearer semantics
- Update review-pr skill: accept docs/adr/, reject agent artifacts

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.codex/skills/implement-task/SKILL.md

@@ -1,16 +1,16 @@
 ---
-name: do-task
+name: implement-task
 description: Phase 2 skill. Use when issue scope is locked by Product Owner (Phase 1 done). Plan, implement, create PR, and own it until merged as Developer.
 ---
 
-# Do Task
+# Implement Task
 
 **Phase:** 2 — Requirement Implementation
 **Role:** Developer
 
 ## When to invoke
 
-- User says: "implement issue #X", "/do-task #X"
+- User says: "implement issue #X", "/implement-task #X"
 - Phase 1 is complete (issue has a "Final Requirements" comment from PO).
 
 ## Prerequisite
@@ -75,6 +75,7 @@ description: Phase 2 skill. Use when issue scope is locked by Product Owner (Pha
 - Never edit remote files directly — always work on local branch.
 - Never claim completion without fresh verification output.
 - Keep changes strictly scoped to the approved plan.
+- If the change needs durable documentation, create/update `docs/adr/**`. Do not commit `docs/superpowers/**` planning artifacts.
 
 ## Next skill
 After PR is created, the user invokes `/review-pr <pr-number>` on the Reviewer agent.

.codex/skills/review-pr/SKILL.md

@@ -104,6 +104,8 @@ Validation:
 - Post review proactively if verdict is clear.
 - Mention validation commands you actually ran.
 - No bracketed author/tool tags.
+- Accept `docs/adr/**` when it records a direct, durable decision tied to the issue scope.
+- Treat `docs/superpowers/**` and other agent execution artifacts as scope creep. When rejecting docs, explain whether the content should be deleted entirely or rewritten as an ADR.
 
 ## What happens next
 - **PASS (APPROVED):** Developer merges the PR.

.codex/skills/validate-issue/SKILL.md

@@ -35,6 +35,7 @@ description: Phase 1 skill. Use when a Gitea issue is created or updated and nee
      - Stop. Wait for user to respond, then re-run this skill.
    - **Clear and feasible:**
      - Post Final Requirements (see format below).
+     - If the change likely needs a durable ADR, add a note: "ADR recommended: this change locks in a behavior/contract that future work must preserve."
      - This locks the scope and signals Phase 2 can begin.
 
 ## Final Requirements format