feat: demo deployment with AIUI chat, SSH key auth, Quick Start fix

- Add AIUI pre-built dist to demo/ for Portainer deployment
- Add nginx-demo.conf with Claude API proxy (envsubst for API key)
- Add docker-entrypoint.sh for runtime API key injection
- Update Dockerfile.web to include AIUI and Claude proxy
- Update docker-compose.demo.yml with ANTHROPIC_API_KEY env var
- Switch deploy script from sshpass to SSH key auth
- Fix Quick Start Goals animating before other cards (stagger 5, opacity guard)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

demo/aiui/images/loading-poster.svg

@@ -0,0 +1,24 @@
+<svg width="200" height="300" viewBox="0 0 200 300" fill="none" xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <clipPath id="clip-poster">
+      <rect width="200" height="300" rx="12" fill="white"/>
+    </clipPath>
+  </defs>
+  <g clip-path="url(#clip-poster)">
+    <rect width="200" height="300" fill="currentColor" fill-opacity="0.15"/>
+    <g fill="currentColor" fill-opacity="0.2">
+      <rect x="8" y="12" width="16" height="24" rx="2"/>
+      <rect x="40" y="12" width="16" height="24" rx="2"/>
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+      <rect x="104" y="12" width="16" height="24" rx="2"/>
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+      <rect x="168" y="12" width="16" height="24" rx="2"/>
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+      <rect x="40" y="48" width="16" height="24" rx="2"/>
+      <rect x="72" y="48" width="16" height="24" rx="2"/>
+      <rect x="104" y="48" width="16" height="24" rx="2"/>
+      <rect x="136" y="48" width="16" height="24" rx="2"/>
+      <rect x="168" y="48" width="16" height="24" rx="2"/>
+    </g>
+  </g>
+</svg>