feat: agent_poller 所有评论/PR 自动附加 [DEV_AGENT_ID] 签名

- agent_poller.py 读取 DEV_AGENT_ID 环境变量（默认 da-01）
- comment/close-issue/create-pr 自动附加 [da-XXXX-XXXX] 签名
- start_dev_agent.sh 启动时设为 da-MMDD-HHmm，token 改为从环境变量读取
- DEV_AGENT.md 文档说明签名机制
- test_step2 修复 trigger=None 边缘情况

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

scripts/agent_poller.py

@@ -22,6 +22,10 @@ import urllib.error
 GITEA_URL = os.environ.get("GITEA_URL", "http://localhost:3000")
 GITEA_REPO = os.environ.get("GITEA_REPO", "pzhang_zywl/document_analyzer")
 GITEA_TOKEN = os.environ.get("GITEA_API_TOKEN", "")
+AGENT_ID = os.environ.get("DEV_AGENT_ID", "da-01")
+
+# Signature appended to all comments / PR bodies
+AGENT_SIG = f"\n\n---\n[{AGENT_ID}]"
 
 BASE = f"{GITEA_URL}/api/v1/repos/{GITEA_REPO}"
 
@@ -74,15 +78,15 @@ def get_issue(num):
 
 
 def comment_issue(num, body):
-    i = _req("POST", f"/issues/{num}/comments", {"body": body})
+    i = _req("POST", f"/issues/{num}/comments", {"body": body + AGENT_SIG})
     print(f"Comment added to #{num}")
     return i
 
 
 def close_issue(num, body=None):
-    """Close an issue, optionally with a final comment."""
+    """Close an issue, optionally with a final comment (signature auto-appended)."""
     if body:
-        comment_issue(num, body)
+        comment_issue(num, body)  # comment_issue already appends AGENT_SIG
     i = _req("PATCH", f"/issues/{num}", {"state": "closed"})
     print(f"Issue #{num} closed")
     return i
@@ -95,7 +99,8 @@ def create_pr(issue_num, branch, body=None):
     issue = _req("GET", f"/issues/{issue_num}")
     title = f"fix: {issue['title']} - Closes #{issue_num}"
     if body is None:
-        body = f"Closes #{issue_num}\n\n{issue.get('body', '')}\n\n🤖 Generated by dev agent"
+        body = f"Closes #{issue_num}\n\n{issue.get('body', '')}"
+    body += AGENT_SIG
     pr = _req("POST", "/pulls", {
         "title": title,
         "head": branch,