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/lib/mocks/handlers.ts

@@ -0,0 +1,93 @@
+import { http, HttpResponse } from "msw";
+import { FIXTURE_DASHBOARD, FIXTURE_WIDGET_DATA } from "./fixtures";
+
+const BASE = process.env.NEXT_PUBLIC_API_BASE_URL || "http://localhost:8080";
+
+export const handlers = [
+  http.get(`${BASE}/api/v1/dashboard`, () => {
+    return HttpResponse.json(FIXTURE_DASHBOARD);
+  }),
+
+  http.get(`${BASE}/api/v1/groups`, () => {
+    return HttpResponse.json(FIXTURE_DASHBOARD.groups);
+  }),
+
+  http.post(`${BASE}/api/v1/groups`, async ({ request }) => {
+    const body = await request.json();
+    const newGroup = {
+      id: crypto.randomUUID(),
+      name: (body as { name: string }).name,
+      sortOrder: FIXTURE_DASHBOARD.groups.length,
+      collapsed: false,
+      services: [],
+      createdAt: new Date().toISOString(),
+      updatedAt: new Date().toISOString(),
+    };
+    return HttpResponse.json(newGroup, { status: 201 });
+  }),
+
+  http.get(`${BASE}/api/v1/services`, () => {
+    const all = [...FIXTURE_DASHBOARD.ungroupedServices, ...FIXTURE_DASHBOARD.groups.flatMap((g) => g.services)];
+    return HttpResponse.json(all);
+  }),
+
+  http.post(`${BASE}/api/v1/services`, async ({ request }) => {
+    const body = await request.json();
+    const newService = {
+      id: crypto.randomUUID(),
+      ...(body as Record<string, unknown>),
+      sortOrder: 0,
+      urls: (body as { urls: Record<string, unknown>[] }).urls.map((u, i) => ({ ...u, id: crypto.randomUUID(), sortOrder: i })),
+      createdAt: new Date().toISOString(),
+      updatedAt: new Date().toISOString(),
+    };
+    return HttpResponse.json(newService, { status: 201 });
+  }),
+
+  http.put(`${BASE}/api/v1/layout`, async ({ request }) => {
+    const body = await request.json();
+    return HttpResponse.json({ ...FIXTURE_DASHBOARD, ...(body as Record<string, unknown>) });
+  }),
+
+  http.post(`${BASE}/api/v1/assets/icons`, async () => {
+    return HttpResponse.json(
+      {
+        id: crypto.randomUUID(),
+        originalName: "icon.png",
+        storedName: "icon-mock.png",
+        mimeType: "image/png",
+        sizeBytes: 1024,
+        publicPath: "/uploads/icons/icon-mock.png",
+        createdAt: new Date().toISOString(),
+      },
+      { status: 201 },
+    );
+  }),
+
+  http.get(`${BASE}/api/v1/widgets`, () => {
+    return HttpResponse.json(FIXTURE_DASHBOARD.widgets);
+  }),
+
+  http.post(`${BASE}/api/v1/widgets`, async ({ request }) => {
+    const body = await request.json();
+    const newWidget = {
+      id: crypto.randomUUID(),
+      ...(body as Record<string, unknown>),
+      sortOrder: FIXTURE_DASHBOARD.widgets.length,
+      createdAt: new Date().toISOString(),
+      updatedAt: new Date().toISOString(),
+    };
+    return HttpResponse.json(newWidget, { status: 201 });
+  }),
+
+  Object.entries(FIXTURE_WIDGET_DATA).map(([widgetId, data]) =>
+    http.get(`${BASE}/api/v1/widgets/${widgetId}/data`, () => {
+      return HttpResponse.json(data);
+    })
+  ),
+
+  http.post(`${BASE}/api/v1/widgets/:widgetId/refresh`, ({ params }) => {
+    const data = FIXTURE_WIDGET_DATA[params.widgetId as string];
+    return HttpResponse.json(data || { widgetId: params.widgetId, status: "fresh", data: {}, fetchedAt: new Date().toISOString() });
+  }),
+].flat();