Add legacy/experimental warnings to src/core and src/morse __init__.py

Both packages now have docstrings stating they are not part of the stable
public API and pointing to src/she/ as the canonical package.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Mircus

src/core/__init__.py

@@ -1 +1,5 @@
+"""LEGACY / EXPERIMENTAL — not part of the stable public API.
 
+The canonical package is ``she`` (``src/she/``).  Code in ``src/core/``
+is retained for reference only and may be removed in a future release.
+"""

src/morse/__init__.py

@@ -1 +1,5 @@
+"""EXPERIMENTAL — not part of the stable public API.
 
+The canonical package is ``she`` (``src/she/``).  Code in ``src/morse/``
+requires PyTorch, numba, sparse, and psutil, and may change or be removed.
+"""