[MugdhoAI]

Summary

• Add the owner-provided Purple Desert clip as a full viewport fixed video behind the Streamlit app.
• Enable autoplay, mute, looping and inline mobile playback with object-fit: cover, no controls and no visible border.
• Bundle a web optimized silent H.264 copy at 2.8 MiB and a poster fallback at 94 KiB.
• Enable Streamlit static serving and use the poster when reduced motion is requested.
• Add an attribution note for the supplied GetLayers asset and a regression test for video markup and media files.

Validation

• 88 tests passed.
• Ruff and git diff --check passed.
• Search evaluation unchanged: MRR 1.0, NDCG@5 0.9516, Recall@5 0.9375.
• Local preview confirmed the video element, static media URLs, and visible content layering. The browser can decode the muted clip and its loop attribute is enabled.

This PR is not merged. The hosted Streamlit app will use the video once the PR is approved and merged.