chore: unify README under Smoo AI brand and voice

[brentrager]

Rebrands the README to the unified Smoo AI brand spec: branded header (logo + name + tagline + flat-square brand-color badges), brand voice, "Part of Smoo AI" section, and consistent footer line.

All real technical content is preserved — install commands, the multi-language table, every code example, the validation/presigned-URL docs, "Built with", contributing, and the MIT license. This is purely a restructure + rephrase for brand consistency.

No docs/ vault in this repo, so nothing else changed.

🤖 Generated with Claude Code

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Latest commit: 8e00d61

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