Use cd block for Noetica npm install

[mdheller]

Summary

Corrects the Noetica formula npm install invocation after macOS validation showed Homebrew was passing chdir: as a literal npm argument.

Observed failure:

npm error path /private/tmp/noetica-.../{chdir: #<Pathname:/opt/homebrew/Cellar/noetica/0.1.0-dev/libexec>}/package.json

Root cause: the formula used:

system Formula["node"].opt_bin/"npm", "install", ..., chdir: libexec

Homebrew passed the final hash-like expression as an argument to npm in this context.

This PR changes it to the Homebrew-safe shape:

cd libexec do
  system Formula["node"].opt_bin/"npm", "install", "--omit=dev", "--ignore-scripts", "--no-audit", "--no-fund"
end

Boundary

• No change to service supervision.
• No brew services path.
• Homebrew remains installer/distribution only.
• Prophet Mesh remains deferred.

Validation target

After merge:

brew update
brew reinstall sourceos-linux/tap/noetica
noetica version
noetica doctor --json
noetica smoke --dry-run
noetica start