feat: Add ADR 004: District Average Schema Design Decisions and update index references
feat: Add ADR 003: District Average Parity Fixture Contract and update related documentation
feat: Introduce decision notes and architecture decision records - Added a new `Decisions.md` file to document the purpose, format, and writing guidance for decision records. - Created an index for decisions in `index.md` to provide easy navigation to decision notes. - Updated the Home and Sidebar to link to the new decision notes instead of specific ADRs. - Removed outdated knowledge components and decision records related to correlation ID audit propagation and related patterns. - Consolidated and organized knowledge base entries, removing obsolete documentation and ensuring clarity in the remaining content.