chore: scaffold Bun workspace monorepo

Sets up the initial project structure: two packages (@kitchen-md/core
and @kitchen-md/bin), shared tsconfig, shared fixtures, per-package
test stubs (unit, integration, smoke), .gitignore, and project
CLAUDE.md with Conventional Commits convention.

packages/bin/tsconfig.json

@@ -0,0 +1,3 @@
+{
+  "extends": "../../tsconfig.json"
+}