feat: add Quart app factory, config loader, and /api/health endpoint

Config reads from env vars (12-factor); .env.example documents defaults.
Health endpoint is liveness-only (no DB/Redis touch). Test added for CI.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/api/__init__.py

@@ -0,0 +1,8 @@
+"""API blueprint registration."""
+
+from quart import Blueprint
+
+from . import health
+
+api_bp = Blueprint("api", __name__, url_prefix="/api")
+api_bp.add_url_rule("/health", view_func=health.get_health, methods=["GET"])

backend/app/api/health.py

@@ -0,0 +1,5 @@
+"""Health endpoint — no DB or Redis touch; just liveness."""
+
+
+async def get_health():
+    return {"status": "ok"}, 200