add SPA config UI, wire media/rss adapters, event-driven layout push

- React SPA: dashboard, data sources CRUD, widgets CRUD, layout builder,
  presets. TanStack Router + Query, shadcn/ui, Vite proxy to :3000
- wire media + rss adapters into polling loop, remove xtb source type
- media adapter: read username/password from headers, proper subsonic auth
- event handler: subscribe to LayoutChanged, push screen update to clients
- fix clippy warnings across workspace (Default impls, collapsible ifs,
  redundant closures, is_none_or, unused imports)

spa/src/components/ui/breadcrumb.tsx

@@ -0,0 +1,122 @@
+import * as React from "react"
+import { Slot } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+import { ChevronRightIcon, MoreHorizontalIcon } from "lucide-react"
+
+function Breadcrumb({ className, ...props }: React.ComponentProps<"nav">) {
+  return (
+    <nav
+      aria-label="breadcrumb"
+      data-slot="breadcrumb"
+      className={cn(className)}
+      {...props}
+    />
+  )
+}
+
+function BreadcrumbList({ className, ...props }: React.ComponentProps<"ol">) {
+  return (
+    <ol
+      data-slot="breadcrumb-list"
+      className={cn(
+        "flex flex-wrap items-center gap-1.5 text-sm wrap-break-word text-muted-foreground",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function BreadcrumbItem({ className, ...props }: React.ComponentProps<"li">) {
+  return (
+    <li
+      data-slot="breadcrumb-item"
+      className={cn("inline-flex items-center gap-1", className)}
+      {...props}
+    />
+  )
+}
+
+function BreadcrumbLink({
+  asChild,
+  className,
+  ...props
+}: React.ComponentProps<"a"> & {
+  asChild?: boolean
+}) {
+  const Comp = asChild ? Slot.Root : "a"
+
+  return (
+    <Comp
+      data-slot="breadcrumb-link"
+      className={cn("transition-colors hover:text-foreground", className)}
+      {...props}
+    />
+  )
+}
+
+function BreadcrumbPage({ className, ...props }: React.ComponentProps<"span">) {
+  return (
+    <span
+      data-slot="breadcrumb-page"
+      role="link"
+      aria-disabled="true"
+      aria-current="page"
+      className={cn("font-normal text-foreground", className)}
+      {...props}
+    />
+  )
+}
+
+function BreadcrumbSeparator({
+  children,
+  className,
+  ...props
+}: React.ComponentProps<"li">) {
+  return (
+    <li
+      data-slot="breadcrumb-separator"
+      role="presentation"
+      aria-hidden="true"
+      className={cn("[&>svg]:size-3.5", className)}
+      {...props}
+    >
+      {children ?? (
+        <ChevronRightIcon />
+      )}
+    </li>
+  )
+}
+
+function BreadcrumbEllipsis({
+  className,
+  ...props
+}: React.ComponentProps<"span">) {
+  return (
+    <span
+      data-slot="breadcrumb-ellipsis"
+      role="presentation"
+      aria-hidden="true"
+      className={cn(
+        "flex size-5 items-center justify-center [&>svg]:size-4",
+        className
+      )}
+      {...props}
+    >
+      <MoreHorizontalIcon
+      />
+      <span className="sr-only">More</span>
+    </span>
+  )
+}
+
+export {
+  Breadcrumb,
+  BreadcrumbList,
+  BreadcrumbItem,
+  BreadcrumbLink,
+  BreadcrumbPage,
+  BreadcrumbSeparator,
+  BreadcrumbEllipsis,
+}