docs: add AGENT.md workflow and local skills

- AGENT.md: role-based issue-driven workflow (PO → Dev → Reviewer)
- CLAUDE.md: points to AGENT.md
- .codex/skills/: validate-issue, do-task, review-pr with phase gates

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

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

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+---
+name: do-task
+description: Use when handling a Gitea issue/task end-to-end, including validation, planning, implementation, PR creation, and review-feedback iteration.
+---
+
+# Do Task
+
+## Overview
+Process a single Gitea issue from analysis to merge-ready PR with explicit decision gates. Prefer Gitea MCP tools for all issue/PR actions.
+
+## Workflow
+
+1. **Load issue**
+   - Read issue by ID from Gitea.
+   - Extract: problem, expected behavior, impact, acceptance checks.
+
+2. **Validate technical correctness**
+   - Verify against current code/docs/tests.
+   - Decide:
+     - **Valid issue** -> continue to planning.
+     - **Not valid / out of scope** -> comment rationale on issue and stop.
+
+3. **If valid: plan and comment**
+   - Create implementation plan using Superpowers planning flow.
+   - Post summary plan to the issue before coding.
+
+4. **Implement**
+   - Use Superpowers execution flow (TDD + verification before completion).
+   - Keep changes scoped strictly to issue requirements.
+
+5. **Create PR**
+   - Open PR from feature branch.
+   - PR description must include:
+     - Summary of changes
+     - Test evidence (exact commands)
+     - `Fixes #<issue-id>` (or `Closes #<issue-id>`)
+   - Add reviewer: `codex`.
+
+6. **Review feedback loop**
+   - Read all feedback.
+   - For each item:
+     - If technically valid -> implement + re-test + reply.
+     - If not valid -> reply with concise technical reasoning.
+   - Do not blindly accept external feedback without verification.
+
+## Required Rules
+- Use Gitea MCP tools first for issue/PR/review operations.
+- Do not use `tea` or other CLI Gitea clients unless MCP is unavailable.
+- Never claim completion without fresh verification output.
+
+## Quick Command Pattern
+- Invoke as: `/do-task <issue-id>`
+- Example: `/do-task 12`