fix: address code review findings for DNS management

- CRITICAL: Change DNS zones endpoint from GET to POST to avoid
  leaking API token in URL query parameters
- HIGH: Add sync.RWMutex to protect dnsProvider field in Server,
  Deployer, and proxy Manager against concurrent read/write races
- HIGH: Capture old DNS provider reference synchronously before
  launching background cleanup goroutine
- HIGH: Use getDNS()/getDNSProviderLocked() accessors instead of
  direct field reads in all DNS operations

web/.svelte-kit/output/server/chunks/toast.js

@@ -0,0 +1,42 @@
+import { w as writable } from "./index3.js";
+function createToastStore() {
+  const { subscribe, update } = writable([]);
+  let counter = 0;
+  function add(message, type = "info", duration = 5e3) {
+    const id = `toast-${++counter}-${Date.now()}`;
+    const toast = { id, message, type, duration };
+    update((toasts2) => [...toasts2, toast]);
+    if (duration > 0) {
+      setTimeout(() => remove(id), duration);
+    }
+    return id;
+  }
+  function remove(id) {
+    update((toasts2) => toasts2.filter((t) => t.id !== id));
+  }
+  function success(message, duration = 5e3) {
+    return add(message, "success", duration);
+  }
+  function error(message, duration = 7e3) {
+    return add(message, "error", duration);
+  }
+  function warning(message, duration = 5e3) {
+    return add(message, "warning", duration);
+  }
+  function info(message, duration = 5e3) {
+    return add(message, "info", duration);
+  }
+  return {
+    subscribe,
+    add,
+    remove,
+    success,
+    error,
+    warning,
+    info
+  };
+}
+const toasts = createToastStore();
+export {
+  toasts as t
+};