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.

.claude/CLAUDE.md

@@ -0,0 +1,12 @@
+# kitchen-md
+
+## Commit Messages
+
+Commit messages must follow the Conventional Commits specification.
+See [CONVENTIONAL-COMMITS.md](../CONVENTIONAL-COMMITS.md) for the full summary and specification.
+
+Format: `<type>[optional scope]: <description>`
+
+Common types: `feat`, `fix`, `docs`, `chore`, `test`, `refactor`, `build`.
+
+Once files are staged, you may create the commit without waiting for the user to ask.