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/card.tsx

@@ -0,0 +1,50 @@
+import * as React from "react";
+import { cn } from "@/lib/utils";
+
+const Card = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div
+      ref={ref}
+      className={cn("rounded-lg bg-card text-card-foreground shadow-border-card", className)}
+      {...props}
+    />
+  ),
+);
+Card.displayName = "Card";
+
+const CardHeader = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn("flex flex-col gap-1.5 p-4", className)} {...props} />
+  ),
+);
+CardHeader.displayName = "CardHeader";
+
+const CardTitle = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn("text-sm font-medium leading-none", className)} {...props} />
+  ),
+);
+CardTitle.displayName = "CardTitle";
+
+const CardDescription = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn("text-xs text-muted-foreground", className)} {...props} />
+  ),
+);
+CardDescription.displayName = "CardDescription";
+
+const CardContent = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn("p-4 pt-0", className)} {...props} />
+  ),
+);
+CardContent.displayName = "CardContent";
+
+const CardFooter = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn("flex items-center p-4 pt-0", className)} {...props} />
+  ),
+);
+CardFooter.displayName = "CardFooter";
+
+export { Card, CardHeader, CardFooter, CardTitle, CardDescription, CardContent };