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

vite.demo.config.ts

@@ -0,0 +1,44 @@
+import { defineConfig } from 'vite';
+import react from '@vitejs/plugin-react';
+import path from 'path';
+
+/**
+ * Per-slice demo build. Slice name comes from `--mode <name>` and selects
+ * the app folder, base path, and output directory.
+ *
+ * Dev:    vite -c vite.demo.config.ts --mode arrangement
+ * Build:  vite build -c vite.demo.config.ts --mode arrangement
+ *         → dist-demo/arrangement/
+ */
+export default defineConfig(({ mode, command }) => {
+  const slice = mode;
+  const appRoot = path.resolve(__dirname, `src/demo/apps/${slice}`);
+
+  return {
+    root: appRoot,
+    // Dev server uses absolute base so HMR/asset URLs work at the root;
+    // production build prefixes assets with /<slice>/ so the bundle is
+    // portable to any nginx location matching that path.
+    base: command === 'build' ? `/${slice}/` : '/',
+    // Mirror Storybook's staticDirs so /brandlogo/, /images/, etc. resolve.
+    publicDir: path.resolve(__dirname, 'brandassets'),
+    plugins: [react()],
+    resolve: {
+      alias: {
+        '@atoms': path.resolve(__dirname, 'src/components/atoms'),
+        '@molecules': path.resolve(__dirname, 'src/components/molecules'),
+        '@organisms': path.resolve(__dirname, 'src/components/organisms'),
+        '@theme': path.resolve(__dirname, 'src/theme'),
+      },
+    },
+    build: {
+      outDir: path.resolve(__dirname, `dist-demo/${slice}`),
+      emptyOutDir: true,
+      sourcemap: true,
+    },
+    server: {
+      port: 5180,
+      open: false,
+    },
+  };
+});