feat(skills): add blueprint skill for multi-session construction planning

skills/blueprint/SKILL.md

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+---
+name: blueprint
+description: >-
+  Turn a one-line objective into a step-by-step construction plan for
+  multi-session, multi-agent engineering projects. Each step has a
+  self-contained context brief so a fresh agent can execute it cold.
+  Includes adversarial review gate, dependency graph, parallel step
+  detection, anti-pattern catalog, and plan mutation protocol.
+  TRIGGER when: user requests a plan, blueprint, or roadmap for a
+  complex multi-PR task, or describes work that needs multiple sessions.
+  DO NOT TRIGGER when: task is completable in a single PR or fewer
+  than 3 tool calls, or user says "just do it".
+origin: community
+---
+
+# Blueprint — Construction Plan Generator
+
+Turn a one-line objective into a step-by-step construction plan that any coding agent can execute cold.
+
+```
+/blueprint myapp "migrate database to PostgreSQL"
+```
+
+## What You Get
+
+A Markdown plan file in `plans/` where every step is independently executable — a fresh agent in a new session can pick up any step without reading prior steps or conversation history:
+
+- **Steps** — each one-PR sized, with task list, rollback strategy, verification commands, and exit criteria
+- **Dependency graph** — which steps can run in parallel, which must be serial
+- **Design decisions** — rationale for key choices, locked against re-litigation
+- **Invariants** — properties verified after every step
+- **Progress log** — single source of truth for execution state across sessions
+- **Review log** — findings from an adversarial review gate
+
+## Installation
+
+```bash
+mkdir -p ~/.claude/skills
+git clone https://github.com/antbotlab/blueprint.git ~/.claude/skills/blueprint
+```
+
+## Usage
+
+```
+/blueprint <project> <objective>
+```
+
+## Key Features
+
+**Cold-start execution** — Every step includes a self-contained context brief. No prior context needed.
+
+**Adversarial review gate** — Every plan is reviewed by a strongest-model sub-agent (e.g., Opus) against a checklist covering completeness, dependency correctness, and anti-pattern detection.
+
+**Branch/PR/CI workflow** — Built into every step. Detects git/gh availability and degrades gracefully to direct mode when absent.
+
+**Parallel step detection** — Dependency graph identifies steps with no shared files or output dependencies.
+
+**Zero runtime risk** — Pure markdown skill. No hooks, no shell scripts, no executable code. No attack surface.
+
+**Plan mutation protocol** — Steps can be split, inserted, skipped, reordered, or abandoned with formal protocols and audit trail.
+
+## Requirements
+
+- Claude Code (for `/blueprint` slash command)
+- Git + GitHub CLI (optional — enables full branch/PR/CI workflow; Blueprint detects absence and auto-switches to direct mode)
+
+## Source
+
+[github.com/antbotlab/blueprint](https://github.com/antbotlab/blueprint) — MIT License