feat: add question bank schema

Made-with: Cursor

src/db/schema/questionBank.ts

@@ -0,0 +1,22 @@
+import { pgTable, uuid, text, integer, timestamp } from 'drizzle-orm/pg-core';
+import { jsonb } from 'drizzle-orm/pg-core';
+import { stackEnum, levelEnum, questionTypeEnum, questionStatusEnum, questionSourceEnum } from './enums.js';
+
+export const questionBank = pgTable('question_bank', {
+  id: uuid('id').primaryKey().defaultRandom(),
+  stack: stackEnum('stack').notNull(),
+  level: levelEnum('level').notNull(),
+  type: questionTypeEnum('type').notNull(),
+  questionText: text('question_text').notNull(),
+  options: jsonb('options').$type<Array<{ key: string; text: string }>>(),
+  correctAnswer: jsonb('correct_answer').$type<string | string[]>().notNull(),
+  explanation: text('explanation').notNull(),
+  status: questionStatusEnum('status').notNull().default('pending'),
+  source: questionSourceEnum('source').notNull(),
+  usageCount: integer('usage_count').notNull().default(0),
+  createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
+  approvedAt: timestamp('approved_at', { withTimezone: true }),
+});
+
+export type QuestionBank = typeof questionBank.$inferSelect;
+export type NewQuestionBank = typeof questionBank.$inferInsert;