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/internal.js

@@ -0,0 +1,14 @@
+import "./chunks/root.js";
+import { s, a, b } from "./chunks/environment.js";
+import { g, o, c, s as s2, a as a2, b as b2 } from "./chunks/internal.js";
+export {
+  g as get_hooks,
+  o as options,
+  s as set_assets,
+  a as set_building,
+  c as set_manifest,
+  b as set_prerendering,
+  s2 as set_private_env,
+  a2 as set_public_env,
+  b2 as set_read_implementation
+};