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/core/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "@kitchen-md/core",
+  "version": "0.0.0",
+  "type": "module",
+  "main": "./src/index.ts",
+  "exports": {
+    ".": "./src/index.ts"
+  },
+  "scripts": {
+    "test": "bun test"
+  }
+}