Scaffold arrangement demo slice with CompareBar wiring

Add a self-contained demo build target for the Providers → Packages →
Comparison flow, deployable as a static SPA at /arrangement/.

- vite.demo.config.ts: per-slice build via --mode, base path flips for
  dev vs prod, output to dist-demo/<slice>/
- src/demo/: shared fixtures (7 providers across verified/tier3/tier2
  with real venue photography from brandassets) + Zustand basket store
  with ?compare= URL persistence
- Verified-provider packages now share the nine canonical Essentials
  line items per FA convention; only Optionals/Extras vary
- App-level CompareBar surfaces "Already added" / "Maximum 3" feedback
  via transient store error
- ProviderCard logo objectFit cover→contain so wide logos don't crop
- npm scripts demo:dev / demo:build, deps zustand + react-router-dom

package.json

@@ -19,6 +19,8 @@
     "test": "vitest run --passWithNoTests",
     "test:watch": "vitest",
     "chromatic": "chromatic --exit-zero-on-changes --build-script-name=build:storybook",
+    "demo:dev": "vite -c vite.demo.config.ts",
+    "demo:build": "vite build -c vite.demo.config.ts",
     "prepare": "husky"
   },
   "dependencies": {
@@ -28,7 +30,9 @@
     "@mui/material": "^5.16.0",
     "@mui/system": "^5.16.0",
     "react": "^18.3.0",
-    "react-dom": "^18.3.0"
+    "react-dom": "^18.3.0",
+    "react-router-dom": "^7.14.1",
+    "zustand": "^5.0.12"
   },
   "devDependencies": {
     "@eslint/js": "^9.39.4",