Move 42 single-module test files into app/modules/*/tests/ directories
while keeping 40 cross-module and infrastructure tests central in tests/.
Hub fixtures (engine, db, client, cleanup) moved to root conftest.py so
both tests/ and module tests inherit them. Update pyproject.toml testpaths
and Makefile TEST_PATHS to discover all test locations.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
