feat: scaffold Flask + React app with schema and JSON error handling

Claude-Session: https://claude.ai/code/session_01M9MLit5Ko3X4s7rzC5Kv7X

backend/tests/__init__.py

@@ -0,0 +1,26 @@
+"""Point the app at a dedicated test database before any test module imports it."""
+import os
+
+import psycopg2
+from psycopg2 import sql
+
+ADMIN_URL = os.environ.get("TEST_ADMIN_DATABASE_URL", "postgresql://postgres:[email protected]:5432/postgres")
+TEST_DATABASE = "books_test"
+
+
+def _ensure_test_database() -> None:
+    conn = psycopg2.connect(ADMIN_URL)
+    conn.autocommit = True  # CREATE DATABASE cannot run inside a transaction
+    try:
+        with conn.cursor() as cur:
+            cur.execute("SELECT 1 FROM pg_database WHERE datname = %s", (TEST_DATABASE,))
+            if cur.fetchone() is None:
+                cur.execute(sql.SQL("CREATE DATABASE {}").format(sql.Identifier(TEST_DATABASE)))
+    finally:
+        conn.close()
+
+
+_ensure_test_database()
+# Assigned, never defaulted: tests TRUNCATE tables, so they must not inherit a real DATABASE_URL.
+os.environ["DATABASE_URL"] = ADMIN_URL.rsplit("/", 1)[0] + "/" + TEST_DATABASE
+os.environ["PASSWORD_PEPPER"] = "test-pepper-0123456789abcdef0123456789abcdef"