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/theme.js

@@ -0,0 +1,27 @@
+import { w as writable, d as derived } from "./index3.js";
+const THEME_KEY = "dw_theme";
+function getInitialMode() {
+  if (typeof localStorage !== "undefined") {
+    const stored = localStorage.getItem(THEME_KEY);
+    if (stored === "light" || stored === "dark" || stored === "system") return stored;
+  }
+  return "system";
+}
+const themeMode = writable(getInitialMode());
+themeMode.subscribe((value) => {
+  if (typeof localStorage !== "undefined") {
+    localStorage.setItem(THEME_KEY, value);
+  }
+});
+derived(themeMode, ($mode) => {
+  if ($mode === "system") {
+    if (typeof window !== "undefined") {
+      return window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
+    }
+    return "light";
+  }
+  return $mode;
+});
+export {
+  themeMode as t
+};