refactor(frontend): restructure project layout and update API schema

Relocate frontend source code from `next-app/` to `frontend/` to align with the new project structure. This includes removing the old Next.js boilerplate files and establishing a cleaner workspace.

Additionally, updates the OpenAPI specification to include support for the `immich` widget type and its corresponding configuration schema.

- Move frontend files to `frontend/`
- Delete obsolete `next-app/` directory and its configuration
- Add `immich` widget type to `openapi.yaml`
- Update `FrontendPlan.md` with dashboard refactor and UX direction

frontend/components/ui/tabs.tsx

@@ -0,0 +1,48 @@
+"use client";
+
+import * as React from "react";
+import * as TabsPrimitive from "@radix-ui/react-tabs";
+import { cn } from "@/lib/utils";
+
+const Tabs = TabsPrimitive.Root;
+
+const TabsList = React.forwardRef<
+  React.ComponentRef<typeof TabsPrimitive.List>,
+  React.ComponentPropsWithoutRef<typeof TabsPrimitive.List>
+>(({ className, ...props }, ref) => (
+  <TabsPrimitive.List
+    ref={ref}
+    className={cn("inline-flex h-10 items-center justify-center rounded-md bg-muted p-1 text-muted-foreground", className)}
+    {...props}
+  />
+));
+TabsList.displayName = TabsPrimitive.List.displayName;
+
+const TabsTrigger = React.forwardRef<
+  React.ComponentRef<typeof TabsPrimitive.Trigger>,
+  React.ComponentPropsWithoutRef<typeof TabsPrimitive.Trigger>
+>(({ className, ...props }, ref) => (
+  <TabsPrimitive.Trigger
+    ref={ref}
+    className={cn(
+      "inline-flex items-center justify-center whitespace-nowrap rounded-sm px-3 py-1.5 text-sm font-medium ring-offset-background transition-all focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 disabled:pointer-events-none disabled:opacity-50 data-[state=active]:bg-background data-[state=active]:text-foreground data-[state=active]:shadow-sm",
+      className,
+    )}
+    {...props}
+  />
+));
+TabsTrigger.displayName = TabsPrimitive.Trigger.displayName;
+
+const TabsContent = React.forwardRef<
+  React.ComponentRef<typeof TabsPrimitive.Content>,
+  React.ComponentPropsWithoutRef<typeof TabsPrimitive.Content>
+>(({ className, ...props }, ref) => (
+  <TabsPrimitive.Content
+    ref={ref}
+    className={cn("mt-2 ring-offset-background focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2", className)}
+    {...props}
+  />
+));
+TabsContent.displayName = TabsPrimitive.Content.displayName;
+
+export { Tabs, TabsList, TabsTrigger, TabsContent };