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/dropdown-menu.tsx

@@ -0,0 +1,54 @@
+"use client";
+
+import * as React from "react";
+import * as DropdownMenuPrimitive from "@radix-ui/react-dropdown-menu";
+import { cn } from "@/lib/utils";
+
+const DropdownMenu = DropdownMenuPrimitive.Root;
+const DropdownMenuTrigger = DropdownMenuPrimitive.Trigger;
+const DropdownMenuGroup = DropdownMenuPrimitive.Group;
+const DropdownMenuSub = DropdownMenuPrimitive.Sub;
+
+const DropdownMenuContent = React.forwardRef<
+  React.ComponentRef<typeof DropdownMenuPrimitive.Content>,
+  React.ComponentPropsWithoutRef<typeof DropdownMenuPrimitive.Content>
+>(({ className, sideOffset = 4, ...props }, ref) => (
+  <DropdownMenuPrimitive.Portal>
+    <DropdownMenuPrimitive.Content
+      ref={ref}
+      sideOffset={sideOffset}
+      className={cn(
+        "z-50 min-w-[8rem] overflow-hidden rounded-md border border-border bg-popover p-1 text-popover-foreground shadow-md data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0 data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95 data-[side=bottom]:slide-in-from-top-2 data-[side=left]:slide-in-from-right-2 data-[side=right]:slide-in-from-left-2 data-[side=top]:slide-in-from-bottom-2",
+        className,
+      )}
+      {...props}
+    />
+  </DropdownMenuPrimitive.Portal>
+));
+DropdownMenuContent.displayName = DropdownMenuPrimitive.Content.displayName;
+
+const DropdownMenuItem = React.forwardRef<
+  React.ComponentRef<typeof DropdownMenuPrimitive.Item>,
+  React.ComponentPropsWithoutRef<typeof DropdownMenuPrimitive.Item> & { inset?: boolean }
+>(({ className, inset, ...props }, ref) => (
+  <DropdownMenuPrimitive.Item
+    ref={ref}
+    className={cn(
+      "relative flex cursor-default select-none items-center gap-2 rounded-sm px-2 py-1.5 text-sm outline-none transition-colors focus:bg-accent focus:text-accent-foreground data-[disabled]:pointer-events-none data-[disabled]:opacity-50 [&_svg]:pointer-events-none [&_svg]:size-4 [&_svg]:shrink-0",
+      inset && "pl-8",
+      className,
+    )}
+    {...props}
+  />
+));
+DropdownMenuItem.displayName = DropdownMenuPrimitive.Item.displayName;
+
+const DropdownMenuSeparator = React.forwardRef<
+  React.ComponentRef<typeof DropdownMenuPrimitive.Separator>,
+  React.ComponentPropsWithoutRef<typeof DropdownMenuPrimitive.Separator>
+>(({ className, ...props }, ref) => (
+  <DropdownMenuPrimitive.Separator ref={ref} className={cn("-mx-1 my-1 h-px bg-border", className)} {...props} />
+));
+DropdownMenuSeparator.displayName = DropdownMenuPrimitive.Separator.displayName;
+
+export { DropdownMenu, DropdownMenuTrigger, DropdownMenuContent, DropdownMenuItem, DropdownMenuSeparator, DropdownMenuGroup, DropdownMenuSub };