clan-app: Add knip dead code analyzer

pkgs/clan-app/ui-2d/package.json

@@ -10,6 +10,7 @@
     "convert-html": "node gtk.webview.js",
     "serve": "vite preview",
     "check": "tsc --noEmit --skipLibCheck && eslint ./src",
+    "knip": "knip",
     "test": "vitest run --project unit --typecheck",
     "storybook": "storybook",
     "storybook-build": "storybook build",
@@ -43,6 +44,7 @@
     "eslint-plugin-tailwindcss": "^3.17.0",
     "http-server": "^14.1.1",
     "jsdom": "^26.1.0",
+    "knip": "^5.61.2",
     "playwright": "~1.52.0",
     "postcss": "^8.4.38",
     "postcss-url": "^10.1.3",