add CliRunner.list_certs()

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

openvpncertupdate.py

@@ -1315,6 +1315,11 @@ class CliRunner:
             sys.exit(1)
         print(f"CRL updated → {CRL_DEST_PATH}")
 
+    def list_certs(self, show_all: bool) -> None:
+        certs = (load_all_certs(EASYRSA_PKI_DIR) if show_all
+                 else load_expiring_certs(EASYRSA_PKI_DIR, DAYS_PAST, DAYS_AHEAD))
+        print(_format_cert_table(certs))
+
     def _issue(self, cn: str, email_addr: str, is_renewal: bool,
                send_email_flag: bool = True, show_eml: bool = False) -> None:
         password = generate_password()