_MEMORY_ROOT was defined independently in reader.py, writer.py, and
index.py. Moved to memory/__init__.py; all three import from there.
Also fixes a bug in append_memory where path.write_text() was called
before path.parent.mkdir(), which would crash when creating a file in
a new subdirectory.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Directory structure, pyproject.toml with hatchling build, and all
subpackage stubs for pyra Stage 1.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
curo1305