Add transport DDL, repos and transport service

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).

data/ddl/09_stations.sql

@@ -0,0 +1,9 @@
+CREATE TABLE IF NOT EXISTS `stations` (
+    `id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
+    `name` VARCHAR(255) NOT NULL,
+    `description` TEXT NULL,
+    `createdAt` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    PRIMARY KEY (id),
+    INDEX idx_stations_name (name)
+);