Add empty __init__.py files to src/mediastorm and all subpackages
(ingest, enrich, vectorize, rag) for explicit Python package declaration.
Ensures proper module discovery and import paths.

Test results: 190 passed, 10 failed (pre-existing failures unrelated to
imports). All test collection errors resolved.

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