Closes #74

Type of Change

• Bug fix (non-breaking change that fixes an issue)

Summary

The fetch call to the AI service in ai-client.ts had no AbortController or timeout configuration. If the AI service hangs, the request blocks indefinitely, holding open sockets and event loop references. Under AI service degradation, this can exhaust available sockets.

This PR adds an AbortController with a configurable timeout (default 30s) via the new AI_TIMEOUT_MS environment variable. Hung connections are now cleaned up and a meaningful error is thrown.

Motivation / Context

Fixes #74 — under AI service degradation, hung fetch connections keep Node.js event loop references and sockets open, which can exhaust resources. The existing fallback in quizService.generateQuiz catches errors and falls back to placeholder questions, but couldn't handle hung connections.

Detailed Changes

src/config/index.ts:

• Added AI_TIMEOUT_MS env var with z.coerce.number().default(30_000) — configurable per environment

src/modules/quizzes/ai-client.ts:

• Wrapped fetch call with AbortController using config.AI_TIMEOUT_MS
• Added signal: controller.signal to the fetch options
• Added catch block to detect AbortError and throw a descriptive timeout error
• Added finally block to clear the timeout timer on success or failure

Testing

• Lint: 0 errors (75 pre-existing warnings)
• Typecheck: passes (pre-existing async-lock module error unrelated)
• Unit tests: 80/80 passing (8 failed suites are pre-existing infra issues — e2e tests requiring Redis/DB)