feat: add static demo site at demo.snapotter.com

- New apps/demo/ that reuses apps/web components with mocked API layer
- Full UI shell: login, change password, analytics consent, dashboard, all tool pages
- Stateful mock tracks session flow (password change, analytics consent)
- Demo banner with link to GitHub repo
- Processing attempts show info message with GitHub link
- Deployed to Cloudflare Pages as static site (no backend)

Also links demo across all surfaces:
- README: "Live Demo" badge
- Landing navbar: "Try Demo" CTA button (replaces "Book a Demo")
- Landing hero: "No sign-ups. No credit card." tagline
- Docs getting-started: "Try before installing" tip box

Other changes:
- Docs: move NVIDIA GPU section above GHCR, demote GHCR to collapsed details
- Fix before-after slider checkerboard background for transparency
- Fix remove-bg preview reset when no effects applied

apps/demo/vite.config.ts

@@ -0,0 +1,21 @@
+import path from "node:path";
+import tailwindcss from "@tailwindcss/vite";
+import react from "@vitejs/plugin-react";
+import { defineConfig } from "vite";
+
+export default defineConfig({
+  plugins: [react(), tailwindcss()],
+  resolve: {
+    alias: {
+      "@": path.resolve(__dirname, "../web/src"),
+    },
+    dedupe: ["react", "react-dom"],
+  },
+  server: {
+    host: true,
+    port: 1352,
+  },
+  build: {
+    outDir: "dist",
+  },
+});