docs(readme): polish GitHub landing page

[jack-arturo]

Summary

• Rework the README into a centered, product-forward GitHub landing page
• Add a public GitHub user-attachments trailer embed
• Tighten install, feature, workflow, tools, and development sections while preserving precise plugin-reuse language

Tests

• git diff --check -- README.md
• Verified README local image path exists
• Verified trailer attachment with unauthenticated range GET: HTTP 206, video/mp4
• Confirmed no tracked .mp4 or trailer/out artifacts

Risk

• Docs-only change; no MCP server or Python behavior changed.

[Copilot]

Pull request overview

Docs-only refresh of the README to present Stream Deck MCP as a centered, product-forward GitHub landing page, with a new demo video embed and tightened install/feature/tools/development sections.

Changes:

• Restructured README with centered header, logo, nav links, and a Demo section embedding a GitHub user-attachments trailer.
• Consolidated install, features, workflows, tools, and skill sections; moved authoring notes and legacy USB mode under Development.
• Added streamdeck_read_plugins and design_streamdeck_deck prompt entries to the tool tables.

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