docs(readme): concise, scannable body under the trailer

[Maxaubert]

Summary

• Everything from the trailer up (icon, name, tagline, badges, links, video) is unchanged.
• The long prose below it is replaced by a short pitch, a features table (nine one-line features), the screenshot row, Install (with the SmartScreen note and requirements), a compact Keys table, Build from source and License.
• Every claim is carried over from the previous README; nothing new is promised. 147 lines down to 88.

Docs only: no code, no version bump.

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