Fix CI: use opencode-ai package for OpenCode install

Author: GitHub Copilot CLI

.devcontainer/Dockerfile

@@ -45,7 +45,7 @@ FROM system-base AS dev-tools
 ENV npm_config_cache=/tmp/npm-cache
 RUN --mount=type=cache,target=/tmp/npm-cache \
     # 並列npm install（依存関係なし）
-    npm install -g --prefer-offline @opencode-ai/cli & \
+    npm install -g --prefer-offline opencode-ai & \
     npm install -g --prefer-offline @openchamber/web & \
     npm install -g --prefer-offline ecc-universal & \
     # 並列処理完了待ち

.devcontainer/setup.sh

@@ -56,7 +56,7 @@ declare -a INSTALL_NAMES=()
 
 if ! command -v opencode &> /dev/null; then
     echo "   OpenCode CLI をインストール中..."
-    npm install -g @opencode-ai/cli &
+    npm install -g opencode-ai &
     INSTALL_PIDS+=("$!")
     INSTALL_NAMES+=("OpenCode CLI")
 else