fix: detect zone name collisions with named.conf main config

创建 zone 时只检查 BIND_CONF_LOCAL 里的重复声明，遗漏了用户在
named.conf 主配置里手动声明的同名 zone —— 后果是 named reload
时直接报 'zone already exists' 错误，named 起不来。

新增 parse_all_managed_zones()，通过 named-checkconf -p 拿到 named
当前加载的所有 zone，区分 source=local（Web UI 管理的）和 source=main
（用户在 named.conf 主配置里写的）。

zone_create() 在写入新声明前检查这两个来源：
- 同名在 BIND_CONF_LOCAL：拒绝并提示
- 同名在 named.conf 主配置：拒绝并提示用户先去主配置里注释掉

回归测试在 dev 环境通过：识别 4 个 builtin zone (source=main) +
3 个 web UI zone (source=local)。

app.py

@@ -216,6 +216,53 @@ def parse_named_conf_local():
     return zones
 
 
+def parse_all_managed_zones():
+    """Return all zone names that BIND currently has loaded (master/slave/in-view),
+    including zones declared in the main named.conf outside BIND_CONF_LOCAL.
+
+    Uses `named-checkconf -p` which prints the fully-resolved configuration with
+    all included files expanded, so we can detect duplicates the user might have
+    added manually (e.g. a zone declared in /etc/named.conf that web UI doesn't
+    know about).
+
+    Returns a dict: zone_name -> {"type": str, "file": str, "source": "local"|"main"}.
+    """
+    rc, out, err = run_cmd("named-checkconf -p 2>&1", timeout=15)
+    if rc != 0:
+        # If named-checkconf fails (e.g. broken config), fall back to local-only
+        # so the UI doesn't break entirely.
+        return {z["name"]: {"type": z["type"], "file": z["file"], "source": "local"}
+                for z in parse_named_conf_local()}
+
+    # Parse the dumped config: zone statements with a non-builtin type (i.e. not
+    # "hint" and not under automatic empty-zones). We deliberately include builtin
+    # zones too and let callers filter.
+    result = {}
+    pattern = re.compile(
+        r'zone\s+"([^"]+)"\s+(?:IN\s+)?\{\s*'
+        r'type\s+(\w+)\s*;\s*'
+        r'(?:file\s+"([^"]+)"\s*;\s*)?',
+        re.MULTILINE,
+    )
+    for m in pattern.finditer(out):
+        name, ztype, zfile = m.group(1), m.group(2), m.group(3) or ""
+        # Skip builtin/hint zones and the "empty" automatic zones (no file).
+        if ztype == "hint" or not zfile:
+            continue
+        result[name] = {"type": ztype, "file": zfile, "source": "unknown"}
+
+    # Mark which ones came from BIND_CONF_LOCAL for the UI to know whether to
+    # let the user edit/delete them.
+    local_names = {z["name"] for z in parse_named_conf_local()}
+    for name in result:
+        if name in local_names:
+            result[name]["source"] = "local"
+        else:
+            result[name]["source"] = "main"
+
+    return result
+
+
 def write_named_conf_local(zones):
     """Rewrite named.conf.local from zone list."""
     lines = ['// Local zone configurations - managed by DNS Web UI\n']
@@ -687,10 +734,22 @@ def zone_create():
 
         zone_file = os.path.join(BIND_ZONES_DIR, f"db.{zone_name}")
 
-        # Check duplicate
+        # Check duplicate — both against zones we manage in BIND_CONF.local AND
+        # against zones declared elsewhere in named.conf (e.g. user manually
+        # added a zone block in /etc/named.conf). Without the second check,
+        # creating a zone with a name already declared in the main config would
+        # produce a duplicate zone error on BIND reload.
         existing = parse_named_conf_local()
+        all_managed = parse_all_managed_zones()
         if any(z["name"] == zone_name for z in existing):
-            flash(f"域名 {zone_name} 已存在", "error")
+            flash(f"域名 {zone_name} 已在 Web UI 中存在", "error")
+            return render_template("zone_form.html")
+        if zone_name in all_managed:
+            flash(
+                f"域名 {zone_name} 已在 named.conf 中声明（不在 Web UI 管理范围内），"
+                f"请先到 named.conf 中注释/删除后再创建",
+                "error",
+            )
             return render_template("zone_form.html")
 
         # Generate initial zone file