feat: worktree 隔离方案 - 多 agent 独立工作目录 - Closes #102

启动 agent 后自动创建 ~/.gitea/worktrees/<user>/ 隔离目录，
多个 agent 可同时修改不同文件、不同分支互不干扰。

- _common.sh: 新增 setup_worktree/cleanup_worktree 函数
- start_dev_agent.sh: 启动时自动切 worktree
- start_qe_agent.sh: 同上
- DEV_AGENT.md/QE_AGENT.md: 启动行为增加 worktree 检查步骤

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

scripts/start_qe_agent.sh

@@ -15,6 +15,12 @@ export GITEA_USER="$1"
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
 source "$SCRIPT_DIR/_common.sh"
 
+# Switch to isolated worktree so multiple agents don't conflict
+setup_worktree "$GITEA_USER"
+
+# Cleanup worktree on exit (optional, comment out to keep for debugging)
+trap 'cleanup_worktree "$GITEA_USER"' EXIT
+
 banner "QE"
 require_token