feat(assistant): add multi-dialog UX, task-aware llm settings, and i18n cleanup

frontend/src/lib/components/layout/Breadcrumbs.svelte

@@ -30,7 +30,7 @@
    */
   function getBreadcrumbs(pathname, maxVisible = 3) {
     const segments = pathname.split("/").filter(Boolean);
-    const allItems = [{ label: "Home", path: "/" }];
+    const allItems = [{ label: $t.nav?.home || "Home", path: "/" }];
 
     let currentPath = "";
     segments.forEach((segment, index) => {
@@ -136,7 +136,7 @@
 
 <nav
   class="mx-4 md:mx-6"
-  aria-label="Breadcrumb navigation"
+  aria-label={$t.nav?.breadcrumb_nav || "Breadcrumb navigation"}
 >
   <div class="inline-flex max-w-full items-center gap-1.5 rounded-xl border border-slate-200/80 bg-white/85 px-2 py-1.5 shadow-sm backdrop-blur">
     {#each breadcrumbItems as item, index}