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/favicon.svg

@@ -0,0 +1,4 @@
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+  <rect width="32" height="32" rx="6" fill="#111111"/>
+  <path d="M 16,5.5 Q 16,16 26.5,16 Q 16,16 16,26.5 Q 16,16 5.5,16 Q 16,16 16,5.5 Z" fill="#fafafa"/>
+</svg>