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/tailwind.config.ts

@@ -0,0 +1,74 @@
+import type { Config } from "tailwindcss";
+
+export default {
+  content: ["./app/**/*.{ts,tsx}", "./components/**/*.{ts,tsx}", "./lib/**/*.{ts,tsx}"],
+  theme: {
+    extend: {
+      fontFamily: {
+        sans: ["var(--font-geist-sans)", "Arial", "sans-serif"],
+        mono: ["var(--font-geist-mono)", "ui-monospace", "monospace"],
+      },
+      colors: {
+        border: "var(--color-border)",
+        background: "var(--color-background)",
+        foreground: "var(--color-foreground)",
+        muted: {
+          DEFAULT: "var(--color-muted)",
+          foreground: "var(--color-muted-foreground)",
+        },
+        accent: {
+          DEFAULT: "var(--color-accent)",
+          foreground: "var(--color-accent-foreground)",
+        },
+        destructive: {
+          DEFAULT: "var(--color-destructive)",
+          foreground: "var(--color-destructive-foreground)",
+        },
+        card: {
+          DEFAULT: "var(--color-card)",
+          foreground: "var(--color-card-foreground)",
+        },
+        popover: {
+          DEFAULT: "var(--color-popover)",
+          foreground: "var(--color-popover-foreground)",
+        },
+        primary: {
+          DEFAULT: "var(--color-primary)",
+          foreground: "var(--color-primary-foreground)",
+        },
+        secondary: {
+          DEFAULT: "var(--color-secondary)",
+          foreground: "var(--color-secondary-foreground)",
+        },
+        signal: "var(--color-signal)",
+      },
+      borderRadius: {
+        lg: "8px",
+        md: "6px",
+        sm: "4px",
+      },
+      boxShadow: {
+        "ring-border": "0px 0px 0px 1px var(--color-border)",
+        "card-stack":
+          "0px 0px 0px 1px var(--color-border), 0px 2px 4px rgba(0,0,0,0.04), 0px 8px 8px -8px rgba(0,0,0,0.04)",
+        "card-hover":
+          "0px 0px 0px 1px var(--color-border), 0px 4px 8px rgba(0,0,0,0.08), 0px 8px 16px -4px rgba(0,0,0,0.08)",
+      },
+      keyframes: {
+        "accordion-down": {
+          from: { height: "0" },
+          to: { height: "var(--radix-accordion-content-height)" },
+        },
+        "accordion-up": {
+          from: { height: "var(--radix-accordion-content-height)" },
+          to: { height: "0" },
+        },
+      },
+      animation: {
+        "accordion-down": "accordion-down 0.2s ease-out",
+        "accordion-up": "accordion-up 0.2s ease-out",
+      },
+    },
+  },
+  plugins: [require("tailwindcss-animate")],
+} satisfies Config;