feat: make BIND paths configurable via env vars (RHEL/CentOS support)

默认路径仍为 Debian/Ubuntu 的 /etc/bind/*。通过环境变量可在 RHEL/CentOS
（默认 /var/named + /etc/named.conf）上运行：

  BIND_CONF_DIR, BIND_ZONES_DIR, BIND_CONF_LOCAL,
  BIND_CONF_OPTIONS, BIND_RNDC_KEY, BIND_SERVICE

README 增加 RHEL/CentOS 安装步骤、systemd Environment 示例，
并提示覆盖 BIND_CONF_LOCAL 后必须在 named.conf 里 include。

Motivation: 同一项目在 CentOS 7 上 zone 文件写不到 /var/named，
Web 端新增域名后 rndc reload 找不到 zone。

app.py

@@ -27,12 +27,16 @@ app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
 db = SQLAlchemy(app)
 
 # ─── BIND paths ───
-BIND_CONF_DIR = "/etc/bind"
-BIND_ZONES_DIR = "/etc/bind/zones"
-BIND_CONF_LOCAL = "/etc/bind/named.conf.local"
-BIND_CONF_OPTIONS = "/etc/bind/named.conf.options"
-BIND_RNDC_KEY = "/etc/bind/rndc.key"
-BIND_SERVICE = "named"
+# Defaults are Debian/Ubuntu (bind9). Override via env on RHEL/CentOS/Rocky:
+#   BIND_CONF_DIR=/etc        BIND_CONF_LOCAL=/etc/named.conf
+#   BIND_ZONES_DIR=/var/named BIND_CONF_OPTIONS=/etc/named.conf.options
+#   BIND_RNDC_KEY=/etc/rndc.key
+BIND_CONF_DIR     = os.environ.get("BIND_CONF_DIR",     "/etc/bind")
+BIND_ZONES_DIR    = os.environ.get("BIND_ZONES_DIR",    "/etc/bind/zones")
+BIND_CONF_LOCAL   = os.environ.get("BIND_CONF_LOCAL",   "/etc/bind/named.conf.local")
+BIND_CONF_OPTIONS = os.environ.get("BIND_CONF_OPTIONS", "/etc/bind/named.conf.options")
+BIND_RNDC_KEY     = os.environ.get("BIND_RNDC_KEY",     "/etc/bind/rndc.key")
+BIND_SERVICE      = os.environ.get("BIND_SERVICE",      "named")
 
 # ─── Record types ───
 RECORD_TYPES = ["A", "AAAA", "CNAME", "MX", "TXT", "NS", "PTR", "SRV", "CAA", "SOA"]
@@ -890,17 +894,17 @@ def record_delete(zone_name, idx):
 def service_control(action):
     u = current_user()
     if action == "start":
-        rc, out, err = run_cmd("systemctl start named 2>&1")
+        rc, out, err = run_cmd("systemctl start named")
         AuditLog.log(u.username, "启动BIND服务")
-        msg = "BIND 服务已启动" if rc == 0 else f"启动失败: {err}"
+        msg = "BIND 服务已启动" if rc == 0 else f"启动失败: {out} {err}"
     elif action == "stop":
-        rc, out, err = run_cmd("systemctl stop named 2>&1")
+        rc, out, err = run_cmd("systemctl stop named")
         AuditLog.log(u.username, "停止BIND服务")
-        msg = "BIND 服务已停止" if rc == 0 else f"停止失败: {err}"
+        msg = "BIND 服务已停止" if rc == 0 else f"停止失败: {out} {err}"
     elif action == "restart":
-        rc, out, err = run_cmd("systemctl restart named 2>&1")
+        rc, out, err = run_cmd("systemctl restart named")
         AuditLog.log(u.username, "重启BIND服务")
-        msg = "BIND 服务已重启" if rc == 0 else f"重启失败: {err}"
+        msg = "BIND 服务已重启" if rc == 0 else f"重启失败: {out} {err}"
     elif action == "reload":
         ok, msg = bind_reload()
         AuditLog.log(u.username, "重载BIND配置")
@@ -934,7 +938,7 @@ def config_view():
         main_content = ""
 
     # Check config
-    rc, out, err = run_cmd("named-checkconf 2>&1")
+    rc, out, err = run_cmd("named-checkconf")
     config_ok = rc == 0
     config_msg = out + err
 
@@ -956,11 +960,11 @@ def config_options_save():
     # Write to temp and validate
     with open("/tmp/named_check.tmp", 'w') as f:
         f.write(content)
-    rc, out, err = run_cmd("named-checkconf /tmp/named_check.tmp 2>&1")
+    rc, out, err = run_cmd("named-checkconf /tmp/named_check.tmp")
     run_cmd("rm -f /tmp/named_check.tmp")
 
     if rc != 0:
-        flash(f"配置验证失败: {err}", "error")
+        flash(f"配置验证失败: {out} {err}", "error")
         return redirect(url_for("config_view"))
 
     with open(BIND_CONF_OPTIONS, 'w') as f:
@@ -986,10 +990,10 @@ def config_local_save():
         f.write(content)
     run_cmd(f"chown root:bind {BIND_CONF_LOCAL}")
 
-    rc, out, err = run_cmd("named-checkconf 2>&1")
+    rc, out, err = run_cmd("named-checkconf")
     if rc != 0:
         run_cmd(f"cp {backup} {BIND_CONF_LOCAL}")
-        flash(f"配置验证失败，已恢复: {err}", "error")
+        flash(f"配置验证失败，已恢复: {out} {err}", "error")
         return redirect(url_for("config_view"))
 
     bind_reload()