feat: add tests for import polling, login page, money utilities, and query keys

- Implemented tests for import polling functionality, ensuring correct behavior for active and terminal import statuses.
- Created tests for the login page, validating user interactions and error handling.
- Added unit tests for money utility functions, covering parsing, formatting, and summation of monetary values.
- Developed tests for query keys, ensuring proper scoping and invalidation roots.

chore: setup testing environment and configuration

- Added setup file for testing with Vitest and Testing Library.
- Configured TypeScript and Vite for the frontend project.
- Created Docker and Nginx configurations for local development and production environments.
- Established a PostgreSQL initialization script for setting up application roles.

docs: add README and environment configuration for infra

- Included README for the infra directory, detailing local development setup and service descriptions.
- Created an example environment configuration file for local development with placeholders for sensitive information.

backend/app/ratelimit.py

@@ -0,0 +1,42 @@
+import hashlib
+import threading
+import time
+from collections import defaultdict, deque
+
+from redis import Redis
+from redis.exceptions import RedisError
+
+from app.config import get_settings
+
+_lock = threading.Lock()
+_hits: dict[str, deque[float]] = defaultdict(deque)
+
+
+def allow(key: str, limit: int, window_seconds: float) -> bool:
+    """Distributed fixed-window limiter with a local fail-safe fallback."""
+    digest = hashlib.sha256(key.encode()).hexdigest()
+    window = int(time.time() // window_seconds)
+    try:
+        client = Redis.from_url(
+            get_settings().redis_url,
+            socket_connect_timeout=0.2,
+            socket_timeout=0.2,
+        )
+        redis_key = f"rate:{digest}:{window}"
+        with client.pipeline() as pipeline:
+            pipeline.incr(redis_key)
+            pipeline.expire(redis_key, int(window_seconds) + 1)
+            count, _ = pipeline.execute()
+        return int(count) <= limit
+    except RedisError:
+        pass
+
+    now = time.monotonic()
+    with _lock:
+        bucket = _hits[digest]
+        while bucket and bucket[0] <= now - window_seconds:
+            bucket.popleft()
+        if len(bucket) >= limit:
+            return False
+        bucket.append(now)
+        return True