feat: ship Claude Code skill in repo with install script

- skill/run-hy3d/SKILL.md: user-level skill now versioned in repo
- skill/install.sh: one-command install to ~/.claude/skills/run-hy3d
- README/README_CN: document skill install/uninstall

skill/install.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+# 安装 hy3d 的 Claude Code skill 到用户级目录（~/.claude/skills/run-hy3d）
+# 用法: ./skill/install.sh
+set -euo pipefail
+
+SRC="$(cd "$(dirname "${BASH_SOURCE[0]}")/run-hy3d" && pwd)"
+DEST="$HOME/.claude/skills/run-hy3d"
+
+mkdir -p "$(dirname "$DEST")"
+rm -rf "$DEST"
+cp -r "$SRC" "$DEST"
+echo "✓ skill 已安装到 $DEST"
+echo "  新会话中即可用 /run-hy3d；描述命中时自动加载"