feat: Sprint 1 — infrastructure + test creation

Backend:
- FastAPI + SQLAlchemy 2.0 async + Alembic
- Models: Test, Question, Answer
- API: GET /api/tests, GET /api/tests/{id}, POST /api/tests
- Pydantic validation: min 7 questions, min 3 answers, ≥1 correct

Frontend:
- React 18 + TypeScript + Vite + Ant Design + TanStack Query
- Pages: TestList, TestCreate (nested Form.List), TestDetail

Infrastructure:
- Docker Compose: db (postgres:16), backend, frontend, nginx
- Nginx: /api/ → FastAPI, / → Vite dev server with HMR
- Alembic migration 001_init: tests, questions, answers tables
- entrypoint.sh: wait for db, migrate, start uvicorn

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/entrypoint.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+set -e
+
+echo "Waiting for PostgreSQL..."
+until pg_isready -h db -p 5432 -U qa_user; do
+  sleep 1
+done
+
+echo "Running migrations..."
+alembic upgrade head
+
+echo "Starting server..."
+exec uvicorn app.main:app --host 0.0.0.0 --port 8000 --reload