docs(readme): swap shields.io badges for shieldcn (light/dark adaptive)

[jal-co]

What

Replaces the four shields.io badges in the README header with shieldcn badges that adapt to the reader's GitHub light/dark theme.

Badge	Before	After
Made by Vercel	static black	branded (auto-contrast text per theme)
NPM version	shields npm/v	branded npm red (auto-contrast text per theme)
License	shields npm/l — rendered "npm not found"	shieldcn github/license → Apache-2.0
Join the community	blueviolet	GitHub purple #43179E

Why

• The existing License badge was broken: img.shields.io/npm/l/eve.svg resolves to a red "npm not found" badge because the npm license field isn't published for eve. Sourcing it from github/license/vercel/eve returns the repo's actual license (Apache-2.0).
• The two brand badges (Made by Vercel, NPM) now follow the reader's GitHub theme via <picture> + prefers-color-scheme, so they stay legible in both light and dark. See shieldcn's light/dark guide.
• shieldcn is a member of the Vercel OSS Program.

How

Only the four badge lines in the README header changed — no other files touched. Brand badges use <picture> with mode=dark/mode=light sources; the color-locked license/community badges remain plain <img> (they look identical in both themes, matching the originals' behavior).

Testing

Both themes verified by rendering each badge SVG at mode=dark and mode=light on GitHub's dark (#0d1117) and light (#ffffff) canvases:

Docs-only / README change — no eve package code touched, so no changeset per CONTRIBUTING.md.

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