feat: visual polish & UX — fade-in, theme toggle, scroll-to-top, footer, cursor, badge

- Add FadeIn component (IntersectionObserver scroll-reveal + load animation)
- Add dark/light theme toggle (useSyncExternalStore + localStorage)
- Add scroll-to-top button (appears after 300px scroll)
- Add configurable footer with social links (gallery.yaml)
- Add crosshair cursor on photo grid items
- Add 'X photos' count badge on subpage cover images
- Add light theme color palette in tokens.css

package.json

@@ -6,7 +6,13 @@
     "dev": "next dev",
     "build": "next build",
     "start": "next start",
-    "lint": "eslint"
+    "lint": "eslint .",
+    "format": "prettier --write .",
+    "format:check": "prettier --check .",
+    "test": "vitest",
+    "test:unit": "vitest run",
+    "test:coverage": "vitest run --coverage",
+    "test:e2e": "playwright test"
   },
   "dependencies": {
     "gray-matter": "^4.0.3",
@@ -14,15 +20,22 @@
     "next": "16.1.6",
     "react": "19.2.3",
     "react-dom": "19.2.3",
-    "thumbhash": "^0.1.1"
+    "thumbhash": "^0.1.1",
+    "zod": "^4.3.6"
   },
   "devDependencies": {
+    "@playwright/test": "^1.58.2",
     "@types/js-yaml": "^4.0.9",
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",
+    "@vitest/coverage-v8": "^4.0.18",
     "eslint": "^9",
     "eslint-config-next": "16.1.6",
-    "typescript": "^5"
+    "eslint-config-prettier": "^10.1.8",
+    "eslint-plugin-prettier": "^5.5.5",
+    "prettier": "^3.8.1",
+    "typescript": "^5",
+    "vitest": "^4.0.18"
   }
 }