feat(frontend): integrate error handling into application

App.svelte:
- Import and render ErrorModal component
- Add ErrorModal to main app layout below Header

CheckIfAniListLoggedInAndLoadWatchList.svelte:
- Import error state helpers (setApiError, clearApiError)
- Wrap LoadAniListUser in try-catch with error handling
- Wrap LoadAniListWatchList in try-catch with error handling
- Update CheckIfAniListLoggedInAndLoadWatchList with error handling
- Remove old alert() calls in favor of modal system

Home.svelte:
- Import isApiDown and apiError stores
- Add conditional rendering for API down state
- Display user-friendly "API Unavailable" message when apiError is set
- Show warning icon and helpful messaging

Error handling is now fully integrated across the frontend application.

frontend/src/helperModules/CheckIfAniListLoggedInAndLoadWatchList.svelte

@@ -12,6 +12,8 @@
     aniListLoggedIn,
     aniListWatchlist,
     aniListSort,
+    clearApiError,
+    setApiError,
   } from "./GlobalVariablesAndHelperFunctions.svelte";
 
   let isAniListPrimary: boolean;
@@ -25,23 +27,55 @@
   aniListSort.subscribe((value) => (sort = value));
 
   export const LoadAniListUser = async () => {
-    await GetAniListLoggedInUser().then((user) => {
-      aniListUser.set(user);
-    });
+    try {
+      await GetAniListLoggedInUser().then((user) => {
+        aniListUser.set(user);
+      });
+    } catch (err) {
+      const errorMsg = err instanceof Error ? err.message : String(err);
+      setApiError(
+        "anilist",
+        `Failed to load user: ${errorMsg}`,
+        undefined,
+        true,
+      );
+      throw err;
+    }
   };
 
   export const LoadAniListWatchList = async () => {
-    await GetAniListUserWatchingList(page, perPage, sort).then((watchList) => {
+    try {
+      const watchList = await GetAniListUserWatchingList(page, perPage, sort);
       aniListWatchlist.set(watchList);
-    });
-  };
-
-  export const CheckIfAniListLoggedInAndLoadWatchList = async () => {
-    const loggedIn = await CheckIfAniListLoggedIn();
-    if (loggedIn) {
-      await LoadAniListUser();
-      if (isAniListPrimary) await LoadAniListWatchList();
+      clearApiError();
+    } catch (err) {
+      const errorMsg = err instanceof Error ? err.message : String(err);
+      setApiError(
+        "anilist",
+        `Failed to load watch list: ${errorMsg}`,
+        undefined,
+        true,
+      );
+      throw err;
+    }
+  };
+  export const CheckIfAniListLoggedInAndLoadWatchList = async () => {
+    try {
+      const loggedIn = await CheckIfAniListLoggedIn();
+      if (loggedIn) {
+        await LoadAniListUser();
+        if (isAniListPrimary) await LoadAniListWatchList();
+      }
+      aniListLoggedIn.set(loggedIn);
+    } catch (err) {
+      const errorMsg = err instanceof Error ? err.message : String(err);
+      setApiError(
+        "anilist",
+        `Authentication failed: ${errorMsg}`,
+        undefined,
+        true,
+      );
+      aniListLoggedIn.set(false);
     }
-    aniListLoggedIn.set(loggedIn);
   };
 </script>