refactor: Make persisted() values raw state

The getter handed out a deep $state proxy, so in-place mutation of a
persisted array/record would update the UI while silently never being
written to localStorage. All consumers already replace .value wholesale;
$state.raw makes that the only semantics and drops the per-read proxy
overhead.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/lib/util/persist.svelte.ts

@@ -37,8 +37,10 @@ export interface Persisted<T> {
 }
 
 // A localStorage-backed reactive value. Reads on init, writes on every set.
+// Raw state: replace `value` wholesale to change it. With a deep proxy,
+// in-place mutation would update the UI without ever being persisted.
 export const persisted = <T>(key: string, initial: T): Persisted<T> => {
-  let value = $state<T>(readJSON(key, initial));
+  let value = $state.raw<T>(readJSON(key, initial));
   return {
     get value() {
       return value;