cli: copy the README before publishing to npm

publish-npm-cli never created packages/cli/README.md, and npm silently
skips a missing files entry, so @cortexkit/magic-context published with
no README and npm shows "No README data found". Mirror publish-npm and
copy the repo README into the package right before npm publish.

Refs #850

Author: trim21

.github/workflows/release.yml

@@ -623,6 +623,9 @@ jobs:
       - name: Build cli
         run: bun run --cwd packages/cli build
 
+      - name: Copy README for npm package
+        run: cp README.md packages/cli/README.md
+
       # Uses npm Trusted Publishing (OIDC) — must be configured on npmjs.com
       # for @cortexkit/magic-context before first release.
       - name: Publish to npm