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/select.tsx

@@ -0,0 +1,82 @@
+"use client";
+
+import * as React from "react";
+import * as SelectPrimitive from "@radix-ui/react-select";
+import { Check, ChevronDown, ChevronUp } from "lucide-react";
+import { cn } from "@/lib/utils";
+
+const Select = SelectPrimitive.Root;
+const SelectGroup = SelectPrimitive.Group;
+const SelectValue = SelectPrimitive.Value;
+
+const SelectTrigger = React.forwardRef<
+  React.ComponentRef<typeof SelectPrimitive.Trigger>,
+  React.ComponentPropsWithoutRef<typeof SelectPrimitive.Trigger>
+>(({ className, children, ...props }, ref) => (
+  <SelectPrimitive.Trigger
+    ref={ref}
+    className={cn(
+      "flex h-9 w-full items-center justify-between gap-2 rounded-md border border-border bg-transparent px-3 py-2 text-sm shadow-sm ring-offset-background placeholder:text-muted-foreground focus:outline-none focus:ring-2 focus:ring-ring disabled:cursor-not-allowed disabled:opacity-50 [&>span]:line-clamp-1",
+      className,
+    )}
+    {...props}
+  >
+    {children}
+    <SelectPrimitive.Icon asChild>
+      <ChevronDown className="h-4 w-4 opacity-50" />
+    </SelectPrimitive.Icon>
+  </SelectPrimitive.Trigger>
+));
+SelectTrigger.displayName = SelectPrimitive.Trigger.displayName;
+
+const SelectContent = React.forwardRef<
+  React.ComponentRef<typeof SelectPrimitive.Content>,
+  React.ComponentPropsWithoutRef<typeof SelectPrimitive.Content>
+>(({ className, children, position = "popper", ...props }, ref) => (
+  <SelectPrimitive.Portal>
+    <SelectPrimitive.Content
+      ref={ref}
+      className={cn(
+        "relative z-50 max-h-96 min-w-[8rem] overflow-hidden rounded-md border border-border bg-popover 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",
+        position === "popper" && "data-[side=bottom]:translate-y-1 data-[side=left]:-translate-x-1 data-[side=right]:translate-x-1 data-[side=top]:-translate-y-1",
+        className,
+      )}
+      position={position}
+      {...props}
+    >
+      <SelectPrimitive.ScrollUpButton className="flex cursor-default items-center justify-center py-1">
+        <ChevronUp className="h-4 w-4" />
+      </SelectPrimitive.ScrollUpButton>
+      <SelectPrimitive.Viewport
+        className={cn("p-1", position === "popper" && "h-[var(--radix-select-trigger-height)] w-full min-w-[var(--radix-select-trigger-width)]")}
+      >
+        {children}
+      </SelectPrimitive.Viewport>
+      <SelectPrimitive.ScrollDownButton className="flex cursor-default items-center justify-center py-1">
+        <ChevronDown className="h-4 w-4" />
+      </SelectPrimitive.ScrollDownButton>
+    </SelectPrimitive.Content>
+  </SelectPrimitive.Portal>
+));
+SelectContent.displayName = SelectPrimitive.Content.displayName;
+
+const SelectItem = React.forwardRef<
+  React.ComponentRef<typeof SelectPrimitive.Item>,
+  React.ComponentPropsWithoutRef<typeof SelectPrimitive.Item>
+>(({ className, children, ...props }, ref) => (
+  <SelectPrimitive.Item
+    ref={ref}
+    className={cn("relative flex w-full cursor-default select-none items-center rounded-sm py-1.5 pl-2 pr-8 text-sm outline-none focus:bg-accent focus:text-accent-foreground data-[disabled]:pointer-events-none data-[disabled]:opacity-50", className)}
+    {...props}
+  >
+    <span className="absolute right-2 flex h-3.5 w-3.5 items-center justify-center">
+      <SelectPrimitive.ItemIndicator>
+        <Check className="h-4 w-4" />
+      </SelectPrimitive.ItemIndicator>
+    </span>
+    <SelectPrimitive.ItemText>{children}</SelectPrimitive.ItemText>
+  </SelectPrimitive.Item>
+));
+SelectItem.displayName = SelectPrimitive.Item.displayName;
+
+export { Select, SelectGroup, SelectValue, SelectTrigger, SelectContent, SelectItem };