docs: additional documentation improvements and cleanup phase 2

Builds on v0.3.0 with additional documentation enhancements from subagent work.

Completed:
- DOC-010: Added Qdrant configuration variables to example env file
- DOC-012: Created CONTRIBUTING.md for developer onboarding
- DOC-013: Created API versioning strategy document
- DOC-009: Verified TODO.md already complete

In Progress:
- DOC-004: CI pipeline patterns documentation
- DOC-005: Security model consolidation
- DOC-008: Architecture diagrams re-rendering
- DOC-011: Deployment decision guide
- DOC-014: Observability documentation

This release continues the comprehensive documentation cleanup effort to transform MD.Hyde from 'planning workspace' to production-ready clinical software with professional documentation standards.

Files changed: 3 files (+935/-2)
Parent release: md-hyde/v0.3.0 (d897e5f)