feat(api): assemble full GameSession with shuffled answer options

Extend the game flow from raw term rows to a complete GameSession
matching the shared schema:

- Add getDistractors model query: fetches N same-POS, same-difficulty,
  same-target-language terms excluding a given termId. Returns bare
  strings since distractors only need their display text.
- Fix getGameTerms select clause to use the neutral field names
  (sourceText, targetText, sourceGloss) that the type already declared.
- Rename gameService entry point to createGameSession; signature now
  takes a GameRequest and returns a GameSession.
- Per question: fetch 3 distractors, combine with the correct answer,
  shuffle (Fisher-Yates), assign optionIds 0-3 by post-shuffle index,
  and assemble into a GameQuestion with a fresh UUID.
- Wrap the questions in a GameSession with its own UUID.
- Run per-question distractor fetches in parallel via Promise.all.

Known gap: the correct option is not yet remembered server-side, so
/game/answer cannot evaluate submissions. SessionStore lands next.

apps/api/src/controllers/gameController.ts

@@ -1,6 +1,6 @@
 import type { Request, Response } from "express";
 import { GameRequestSchema } from "@glossa/shared";
-import { prepareGameQuestions } from "../services/gameService.js";
+import { createGameSession } from "../services/gameService.js";
 
 export const createGame = async (req: Request, res: Response) => {
   const gameSettings = GameRequestSchema.safeParse(req.body);
@@ -11,7 +11,7 @@ export const createGame = async (req: Request, res: Response) => {
     return;
   }
 
-  const gameQuestions = await prepareGameQuestions(gameSettings.data);
+  const gameQuestions = await createGameSession(gameSettings.data);
 
   res.json({ success: true, data: gameQuestions });
 };