feat: shadcn -> rust-ui.com migration + TorrentDetail silme

- Tüm leptos-shadcn-* paketleri kaldırıldı (19 dependency)
- leptos_ui, tw_merge, strum eklendi
- components/ui/ modülü oluşturuldu (Button, Card, Input)
- TorrentDetail bileşeni tamamen silindi
- sidebar.rs: saf HTML+Tailwind ile SidebarButton yardımcı bileşeni
- toolbar.rs, login.rs, setup.rs, add_torrent.rs: saf HTML+Tailwind
- table.rs: shadcn Card -> rust-ui Card
- app.rs: Skeleton -> animate-pulse div

frontend/src/components/ui/card.rs

@@ -0,0 +1,15 @@
+use leptos::prelude::*;
+use leptos_ui::clx;
+
+mod components {
+    use super::*;
+
+    clx! {Card, div, "bg-card text-card-foreground flex flex-col gap-4 rounded-xl border py-6 shadow-sm"}
+    clx! {CardHeader, div, "@container/card-header flex flex-col items-start gap-1.5 px-6 [.border-b]:pb-6"}
+    clx! {CardTitle, h2, "leading-none font-semibold"}
+    clx! {CardContent, div, "px-6"}
+    clx! {CardDescription, p, "text-muted-foreground text-sm"}
+    clx! {CardFooter, footer, "flex items-center px-6 [.border-t]:pt-6", "gap-2"}
+}
+
+pub use components::*;