This commit finalizes the documentation improvement plan by:
- Centralizing reference material in README.md.
- Creating a dedicated Technical Maintenance guide (docs/howtos/maintenance.md).
- Creating a categorized Sample Queries & Mutations overview (docs/queries/README.md).
- Eliminating redundant information across the doc set (DRY principle).
- Optimizing cross-references between reference documentation and the Cookbook.
- Updating the improvement plan to reflect all tasks as completed.
