feat(shared): add quiz session Zod schemas

Add the shared schemas for the quiz request/response cycle, defining
the contract between the API and the frontend.

- Reorganise packages/shared: move schemas into a schemas/ subdirectory
  grouped by domain. Delete the old flat schema.ts.
- Add AnswerOption, GameQuestion, GameSession, AnswerSubmission, and
  AnswerResult alongside the existing GameRequest.
- optionId is an integer 0-3 (positional, shuffled at session-build
  time so position carries no information).
- questionId and sessionId are UUIDs (globally unique, opaque, natural
  keys for Valkey storage later).
- gloss is  rather than optional, for a predictable
  shape on the frontend.
- options array enforced to exactly 4 elements at the schema level.

packages/shared/src/index.ts

@@ -1,2 +1,2 @@
 export * from "./constants.js";
-export * from "./schema.js";
+export * from "./schemas/game.js";

packages/shared/src/schema.ts

@@ -1,18 +0,0 @@
-import * as z from "zod";
-
-import {
-  SUPPORTED_LANGUAGE_CODES,
-  SUPPORTED_POS,
-  GAME_ROUNDS,
-  DIFFICULTY_LEVELS,
-} from "./constants.js";
-
-export const GameRequestSchema = z.object({
-  source_language: z.enum(SUPPORTED_LANGUAGE_CODES),
-  target_language: z.enum(SUPPORTED_LANGUAGE_CODES),
-  pos: z.enum(SUPPORTED_POS),
-  difficulty: z.enum(DIFFICULTY_LEVELS),
-  rounds: z.enum(GAME_ROUNDS),
-});
-
-export type GameRequestType = z.infer<typeof GameRequestSchema>;

packages/shared/src/schemas/game.ts

@@ -0,0 +1,57 @@
+import * as z from "zod";
+
+import {
+  SUPPORTED_LANGUAGE_CODES,
+  SUPPORTED_POS,
+  GAME_ROUNDS,
+  DIFFICULTY_LEVELS,
+} from "../constants.js";
+
+export const GameRequestSchema = z.object({
+  source_language: z.enum(SUPPORTED_LANGUAGE_CODES),
+  target_language: z.enum(SUPPORTED_LANGUAGE_CODES),
+  pos: z.enum(SUPPORTED_POS),
+  difficulty: z.enum(DIFFICULTY_LEVELS),
+  rounds: z.enum(GAME_ROUNDS),
+});
+
+export type GameRequest = z.infer<typeof GameRequestSchema>;
+
+export const AnswerOptionSchema = z.object({
+  optionId: z.number().int().min(0).max(3),
+  text: z.string().min(1),
+});
+
+export type AnswerOption = z.infer<typeof AnswerOptionSchema>;
+
+export const GameQuestionSchema = z.object({
+  questionId: z.uuid(),
+  prompt: z.string().min(1),
+  gloss: z.string().min(1).nullable(),
+  options: z.array(AnswerOptionSchema).length(4),
+});
+
+export type GameQuestion = z.infer<typeof GameQuestionSchema>;
+
+export const GameSessionSchema = z.object({
+  sessionId: z.uuid(),
+  questions: z.array(GameQuestionSchema),
+});
+
+export type GameSession = z.infer<typeof GameSessionSchema>;
+
+export const AnswerSubmissionSchema = z.object({
+  sessionId: z.uuid(),
+  questionId: z.uuid(),
+  selectedOptionId: z.number().int().min(0).max(3),
+});
+
+export type AnswerSubmission = z.infer<typeof AnswerSubmissionSchema>;
+
+export const AnswerResultSchema = z.object({
+  questionId: z.uuid(),
+  isCorrect: z.boolean(),
+  correctOptionId: z.number().int().min(0).max(3),
+});
+
+export type AnswerResult = z.infer<typeof AnswerResultSchema>;