docs: Fix environment variable usage examples in README

Correct the environment variable usage examples to download the script first,
then execute with environment variables. Direct piping does not pass
environment variables to the downloaded script.

Before (incorrect):
NABLEDGE_BRANCH=test-to curl -sSL ... | bash

After (correct):
curl -sSL ... -o setup.sh
NABLEDGE_BRANCH=test-to bash setup.sh

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kiyotis

.claude/skills/nabledge-6/plugin/README.md

@@ -57,10 +57,12 @@ curl -sSL https://raw.githubusercontent.com/nablarch/nabledge/main/setup-6-cc.sh
 
 ```bash
 # テストブランチを使用する場合
-NABLEDGE_BRANCH=test-to curl -sSL https://raw.githubusercontent.com/nablarch/nabledge/main/setup-6-cc.sh | bash
+curl -sSL https://raw.githubusercontent.com/nablarch/nabledge/main/setup-6-cc.sh -o setup.sh
+NABLEDGE_BRANCH=test-to bash setup.sh
 
 # フォーク版を使用する場合
-NABLEDGE_REPO=mycompany/nabledge-fork NABLEDGE_BRANCH=custom curl -sSL https://raw.githubusercontent.com/mycompany/nabledge-fork/custom/setup-6-cc.sh | bash
+curl -sSL https://raw.githubusercontent.com/mycompany/nabledge-fork/custom/setup-6-cc.sh -o setup.sh
+NABLEDGE_REPO=mycompany/nabledge-fork NABLEDGE_BRANCH=custom bash setup.sh
 ```
 
 ### GitHub Copilot
@@ -84,10 +86,12 @@ curl -sSL https://raw.githubusercontent.com/nablarch/nabledge/main/setup-6-ghc.s
 
 ```bash
 # テストブランチを使用する場合
-NABLEDGE_BRANCH=test-to curl -sSL https://raw.githubusercontent.com/nablarch/nabledge/main/setup-6-ghc.sh | bash
+curl -sSL https://raw.githubusercontent.com/nablarch/nabledge/main/setup-6-ghc.sh -o setup.sh
+NABLEDGE_BRANCH=test-to bash setup.sh
 
 # フォーク版を使用する場合
-NABLEDGE_REPO=mycompany/nabledge-fork NABLEDGE_BRANCH=custom curl -sSL https://raw.githubusercontent.com/mycompany/nabledge-fork/custom/setup-6-ghc.sh | bash
+curl -sSL https://raw.githubusercontent.com/mycompany/nabledge-fork/custom/setup-6-ghc.sh -o setup.sh
+NABLEDGE_REPO=mycompany/nabledge-fork NABLEDGE_BRANCH=custom bash setup.sh
 ```
 
 ## 使い方