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/state.svelte.js

@@ -0,0 +1,19 @@
+import "clsx";
+import { n as noop } from "./index.js";
+import "./exports.js";
+import "@sveltejs/kit/internal/server";
+import "./root.js";
+const is_legacy = noop.toString().includes("$$") || /function \w+\(\) \{\}/.test(noop.toString());
+const placeholder_url = "a:";
+if (is_legacy) {
+  ({
+    data: {},
+    form: null,
+    error: null,
+    params: {},
+    route: { id: null },
+    state: {},
+    status: -1,
+    url: new URL(placeholder_url)
+  });
+}