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

pnpm-lock.yaml

@@ -218,6 +218,40 @@ importers:
         specifier: ^5.7.0
         version: 5.9.3
 
+  apps/demo:
+    dependencies:
+      '@snapotter/shared':
+        specifier: workspace:*
+        version: link:../../packages/shared
+      react:
+        specifier: ^19.0.0
+        version: 19.2.4
+      react-dom:
+        specifier: ^19.0.0
+        version: 19.2.4(react@19.2.4)
+    devDependencies:
+      '@tailwindcss/vite':
+        specifier: ^4.0.0
+        version: 4.2.2(vite@6.4.1(@types/node@22.19.15)(jiti@2.6.1)(lightningcss@1.32.0)(terser@5.47.1)(tsx@4.21.0)(yaml@2.8.3))
+      '@types/react':
+        specifier: ^19.0.0
+        version: 19.2.14
+      '@types/react-dom':
+        specifier: ^19.0.0
+        version: 19.2.3(@types/react@19.2.14)
+      '@vitejs/plugin-react':
+        specifier: ^4.3.0
+        version: 4.7.0(vite@6.4.1(@types/node@22.19.15)(jiti@2.6.1)(lightningcss@1.32.0)(terser@5.47.1)(tsx@4.21.0)(yaml@2.8.3))
+      tailwindcss:
+        specifier: ^4.0.0
+        version: 4.2.4
+      typescript:
+        specifier: ^5.7.0
+        version: 5.9.3
+      vite:
+        specifier: ^6.0.0
+        version: 6.4.1(@types/node@22.19.15)(jiti@2.6.1)(lightningcss@1.32.0)(terser@5.47.1)(tsx@4.21.0)(yaml@2.8.3)
+
   apps/docs:
     devDependencies:
       tsx: