feat: add integration tests and seed script for Azure Storage emulator

- scripts/seed_test_data.py: seeds 45 orders (30 Recived + 15 Payed) across
  5 users and 3 days into the emulator
- tests/test_integration.py: full pipeline test (seed → scan → backup → delete)
  with table cleanup before/after
- pytest marker "integration" to separate from unit tests

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

pyproject.toml

@@ -21,3 +21,8 @@ packages = ["src/order_bak"]
 dev = [
     "pytest>=8.0",
 ]
+
+[tool.pytest.ini_options]
+markers = [
+    "integration: integration tests requiring Azure Storage emulator",
+]