Missing documentation files for MRP Purchase Orders feature

[taylorvalton]

During the PR #45 merge audit, several documentation files were found to be missing from the repository:

1. docs/SOP_INTERNAL_V3.4.md
2. docs/SOP_UAT_V3.2.md
3. docs/modules/procurement/README.md

These files are referenced in the test plan but do not exist in the repository. They should be added to complete the audit and provide proper documentation for the new MRP Purchase Orders feature.