Ship a py.typed marker so type checkers use the package's inline types #63

Problem

knowledge_mapper has no py.typed marker (PEP 561). Type checkers treat the installed package as untyped:

• mypy reports Skipping analyzing "knowledge_mapper": module is installed, but missing library stubs or py.typed marker [import-untyped] and infers everything from the package as Any.
• Pyright/Pylance infer types from source anyway, but in strict mode they also treat the package as partially typed.

As a result, the typed APIs (e.g. AskKI[M] / PostKI[A, R] from #62, BindingModel fields, handler signatures) give no static checking for mypy users.

Proposal

• Add an empty src/knowledge_mapper/py.typed.
• Make sure the build backend includes it in the wheel/sdist (check [tool.setuptools.package-data] or equivalent in pyproject.toml).
• Verify: install the built wheel in a fresh env and run mypy on a small script that imports knowledge_mapper; the import-untyped error should be gone.

Notes

Found while verifying #57 / #62.