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

src/components/molecules/ProviderCard/ProviderCard.tsx

@@ -172,7 +172,10 @@ export const ProviderCard = React.forwardRef<HTMLDivElement, ProviderCardProps>(
                   width: LOGO_SIZE,
                   height: LOGO_SIZE,
                   borderRadius: LOGO_BORDER_RADIUS,
-                  objectFit: 'cover',
+                  // 'contain' so wide/tall logos scale proportionally inside
+                  // the square slot rather than cropping. Background fills any
+                  // letterboxed space so it still reads as a tile.
+                  objectFit: 'contain',
                   backgroundColor: 'background.paper',
                   boxShadow: 'var(--fa-shadow-sm)',
                   border: '2px solid var(--fa-color-white)',