feat(db): add PostgreSQL connection and schema definitions

databases/schema.ts

@@ -0,0 +1,32 @@
+import {
+  date,
+  integer,
+  pgTable,
+  serial,
+  text,
+} from "npm:drizzle-orm/pg-core";
+
+export const promotions = pgTable("promotions", {
+  id: serial("id").primaryKey(),
+  endyear: integer("endyear"),
+  current: integer("current"),
+});
+
+export const students = pgTable("students", {
+  userId: text("userId").primaryKey(),
+  firstName: text("firstName"),
+  lastName: text("lastName"),
+  mail: text("mail"),
+  promotionId: integer("promotionId").references(() => promotions.id),
+});
+
+export const mobility = pgTable("mobility", {
+  id: serial("id").primaryKey(),
+  studentId: text("studentId").references(() => students.userId),
+  startDate: date("startDate"),
+  endDate: date("endDate"),
+  weeksCount: integer("weeksCount"),
+  destinationCountry: text("destinationCountry"),
+  destinationName: text("destinationName"),
+  mobilityStatus: text("mobilityStatus").default("N/A"),
+});