Polish README for professional project presentation

[ocularminds]

Summary

• reposition Procuator as a governed, autonomous procurement decisioning system
• document the APPROVE / REFER / DENY lifecycle and five-agent watsonx Orchestrate architecture
• distinguish implemented controls from the planned pricing-drift integration
• replace stale placeholders with real screenshots, repository evidence, and reproducible setup instructions
• document production boundaries without overstating the proof of concept

Validation

• all 30 local README links resolve
• markdownlint passes with MD013 disabled for prose and tables
• pytest -q apps/api/tests — 22 passed
• ruff check apps/api/src apps/api/tests
• ruff format --check apps/api/src apps/api/tests
• npm --prefix apps/web run lint
• npm --prefix apps/web run build

Review note

This is a documentation-only PR stacked on #1 so its diff remains limited to README.md and can reference the feature-oriented paths introduced there.