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/__init__.py

@@ -0,0 +1,19 @@
+"""Quart app factory."""
+
+import logging
+
+from quart import Quart
+
+from .api import api_bp
+from .config import get_config
+
+
+def create_app() -> Quart:
+    cfg = get_config()
+    logging.basicConfig(level=cfg.log_level)
+
+    app = Quart(__name__)
+    app.secret_key = cfg.secret_key
+    app.register_blueprint(api_bp)
+
+    return app