feat: merge cartsnitch/api into api/ subdirectory

Consolidate API gateway service into monorepo.
Squashed from https://github.com/cartsnitch/api main (89bacb1).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

tests/test_middleware/conftest.py

@@ -0,0 +1,19 @@
+"""Conftest for middleware tests — re-enables rate limiting after global disable."""
+
+import pytest
+
+from cartsnitch_api.config import settings as cartsnitch_settings
+
+
+@pytest.fixture(autouse=True)
+def enable_rate_limiting():
+    """Re-enable rate limiting after the global disable_rate_limiting fixture runs.
+
+    The root conftest disables rate limiting for all tests to prevent 429
+    interference. Middleware tests need it active to verify headers and
+    enforcement. This fixture runs after the root fixture (more local = later
+    in setup order) so True is the effective value during the test body.
+    """
+    cartsnitch_settings.rate_limit_enabled = True
+    yield
+    cartsnitch_settings.rate_limit_enabled = False