chore(marketplace): add karpathy-guidelines-plugin, update dev-coding/dev-review/review-checklist

Karpathy 四原则融合到 req 技能工作流 (REQ-20260421-0003):
- dev-coding: 新增 Step 0「验证优先」(Goal-Driven Execution)
- dev-review: 五视角 → 六视角，新增 Scope 审计者 (Simplicity + Surgical)
- review-checklist/general: 新增 Karpathy 反模式速查表
- karpathy-guidelines-plugin: 新增独立插件，含四原则全文 + 与 req 工作流映射

skills-dev/karpathy-guidelines-plugin/.claude-plugin/plugin.json

@@ -0,0 +1,9 @@
+{
+  "name": "karpathy-guidelines",
+  "description": "Karpathy 四原则编码行为守则（Think Before Coding / Simplicity First / Surgical Changes / Goal-Driven Execution）。已深度融合到 req 技能工作流各阶段，可独立激活用于任意编码场景。",
+  "version": "1.0.0",
+  "author": "qiudl",
+  "source": "https://github.com/forrestchang/andrej-karpathy-skills",
+  "tags": ["coding-guidelines", "karpathy", "simplicity", "surgical", "goal-driven"],
+  "skills": ["karpathy-guidelines"]
+}