Add hero selection SVG and include it in README

[StringKe]

Motivation

• Provide a clear, high-resolution hero visual that communicates the project’s core idea: author standards once and sync to multiple AI CLI targets.
• Surface the visual near the top of the README so the value proposition is visible immediately on the project page.

Description

• Add a new scalable asset at assets/hero-selection.svg that shows the project title, a grid of the 11 supported targets, and a central "SYNC" visual focal point.
• Insert an image reference into README.md just below the header separator so the hero appears at the top of the document.
• No code paths, binaries, or runtime behavior were changed by this PR.

Testing

• Verified repository files using rg --files and inspected a subset with rg --files | head -n 200, which completed successfully.
• Confirmed the README now contains the inserted image reference by printing the top lines with nl -ba README.md | sed -n '1,40p', which showed the new asset line.
• Printed the new SVG contents with nl -ba assets/hero-selection.svg | sed -n '1,220p' to validate the generated SVG, which also completed successfully.

---

Codex Task