feat: cat 完全放行，不再限制路径

- 移除 _SAFE_CAT_FILES / _SAFE_CAT_DIRS / _is_safe_cat_path 及相关检查
- cat 在 SHELL_READ_ONLY_COMMANDS 为 None（任意参数均可）
- cat /etc/shadow 等所有路径现在都能正常通过

tests/test_agent_tools.py

@@ -112,13 +112,16 @@ class ShellCommandPolicyTest(unittest.TestCase):
             classify_shell_command("crictl ps -a && sh -c 'echo x'")
 
     def test_cat_only_allows_safe_paths(self):
+        # cat 完全放行，任意路径均可
         decision = classify_shell_command("cat /etc/os-release")
         self.assertEqual(decision.mode, "read")
         self.assertFalse(decision.requires_approval)
 
     def test_cat_rejects_unsafe_path(self):
-        with self.assertRaises(ValueError):
-            classify_shell_command("cat /etc/shadow")
+        # cat 不再限制路径
+        decision = classify_shell_command("cat /etc/shadow")
+        self.assertEqual(decision.mode, "read")
+        self.assertFalse(decision.requires_approval)
 
 
 class EtcdCommandPolicyTest(unittest.TestCase):