Add database DDL and server-side data access/service layers for transport domain. New SQL DDL files create transport_types, lines, stations, platforms and platform_lines tables (with FKs, indexes, spatial POINT column, CHECK constraints, and triggers to populate location). New repositories implement queries and CRUD for lines, stations, platforms and platform_lines (including distance/nearest-platform and accessibility queries). A transportService aggregates repo functions and exposes high-level operations (CRUD, station/line lookups, platform-line management and nearest-platform validation).
