chore: init project skeleton

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>

src/pyra/__init__.py

@@ -0,0 +1 @@
+__version__ = "0.1.0"

src/pyra/__main__.py

@@ -0,0 +1,4 @@
+from pyra.cli import main
+
+if __name__ == "__main__":
+    main()