feat: initialize Lux package registry

- Add registry README with API documentation
- Add initial packages: json, http-client, testing
- Add package index.json for registry server

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/http-client/lux.toml

@@ -0,0 +1,8 @@
+[project]
+name = "http-client"
+version = "0.1.0"
+description = "HTTP client utilities for Lux"
+authors = ["Lux Core Team"]
+license = "MIT"
+
+[dependencies]