feat: add Drizzle ORM support and update README with environment setup and migration scripts

Backend/db/schema.ts

@@ -0,0 +1,8 @@
+import { pgTable, timestamp, uuid, varchar } from 'drizzle-orm/pg-core';
+
+export const users = pgTable('users', {
+  id: uuid('id').defaultRandom().primaryKey(),
+  email: varchar('email', { length: 255 }).notNull().unique(),
+  name: varchar('name', { length: 255 }).notNull(),
+  createdAt: timestamp('created_at', { withTimezone: true }).defaultNow().notNull(),
+});