feat: persist API keys across restarts via tauri-plugin-store

Keys are saved to keys.json in the app's private data directory
on both Linux and Android. load_keys is called on app mount to
restore them into NewsState before the first news fetch.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/pages/news.rs

@@ -69,11 +69,12 @@ pub fn news() -> Html {
     let new_url_ref = use_node_ref();
     let new_cat_ref = use_node_ref();
 
-    // Init: RSS Feeds laden
+    // Init: Keys und RSS Feeds laden
     {
         let rss_feeds = rss_feeds.clone();
         use_effect_with((), move |_| {
             spawn_local(async move {
+                let _ = invoke("load_keys", JsValue::NULL).await;
                 if let Ok(res) = invoke("load_rss_config", JsValue::NULL).await {
                     if let Ok(feeds) = serde_wasm_bindgen::from_value::<Vec<RssFeed>>(res) {
                         rss_feeds.set(feeds);