refactor(frontend): Svelte 5 mount API, router v5, dependency-free table

main.ts uses mount() instead of the legacy constructor. App.svelte
follows svelte-spa-router v5: the removed loc store becomes
router.location, while wrap/push/link keep their v4 call shapes.

AnimeTable.svelte drops svelte-headless-table and reimplements the
same 11 sortable columns (WebsiteLink id cells, asc/desc
indicators, click toggles through asc/desc/off) with local
$state/$derived - about 120 lines, no dependency, fully covered by
svelte-check instead of the libs view model.

frontend/src/App.svelte

@@ -21,13 +21,13 @@
   import { CheckIfMALLoggedInAndSetUser } from "./helperModules/CheckIfMyAnimeListLoggedIn.svelte";
   import { CheckIfSimklLoggedInAndSetUser } from "./helperModules/CheckIsSimklLoggedIn.svelte";
   import {App} from "../bindings/AniTrack";
-  import { loc } from "svelte-spa-router";
+  import { router } from "svelte-spa-router";
   import ErrorModal from "./helperComponents/ErrorModal.svelte";
 
   onMount(async () => {
-    let isAniListLoggedIn: boolean;
-    let isMALLoggedIn: boolean;
-    let isSimklLoggedIn: boolean;
+    let isAniListLoggedIn!: boolean;
+    let isMALLoggedIn!: boolean;
+    let isSimklLoggedIn!: boolean;
     aniListLoggedIn.subscribe((value) => (isAniListLoggedIn = value));
     malLoggedIn.subscribe((value) => (isMALLoggedIn = value));
     simklLoggedIn.subscribe((value) => (isSimklLoggedIn = value));
@@ -39,7 +39,7 @@
     !isSimklLoggedIn && (await CheckIfSimklLoggedInAndSetUser());
   });
 
-  $: if ($loc?.location === "/" && $watchlistNeedsRefresh) {
+  $: if (router.location === "/" && $watchlistNeedsRefresh) {
     (async () => {
       if ($aniListLoggedIn && $aniListPrimary) {
         await CheckIfAniListLoggedInAndLoadWatchList();