Add GDI v3.0 specification: Section 04, Gate Taxonomy layout fix, References

- Bump version to v3.0 across all pages
- Add Section 04: The Governed Decision Record as a standalone labeled section
- Fix Section 05 page break: Gate Taxonomy table no longer splits across pages
- Update Table of Contents: Section 04 added, Section 15 added
- Add Section 15: References and Bibliography

Author: mj3b