feat(#27): Gate B [07/10]: FastAPI health endpoint + app factory (H-1)

- App factory pattern (FUND-8): create_app() produces fresh app per test
- Logging config (structured, no secrets)
- Config validation: SLAB_AES_KEY required, WOO_BASE_URL HTTPS-only
- GET /api/health returns 200 {status: ok, version, woo_reachable: false}
- SQLite + alembic skeleton: full DATA-MODEL schema, initial migration
- API contract tests via httpx TestClient: 5 cases all green
  - test_returns_200, test_returns_ok_status, test_woo_reachable_false
  - test_response_shape, test_with_test_client_lifespan (FUND-9/10)

backend/alembic.ini

@@ -0,0 +1,45 @@
+# Alembic configuration for SlabUploader
+
+[alembic]
+script_location = alembic
+sqlalchemy.url = sqlite:///data/slab.db
+
+# Templates used to generate migration files
+file_template = %%(year)s_%%(month)s_%%(day)s_%%(rev)s_%%(slug)s
+
+# Timezone for file timestamps
+timezone = UTC
+
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARN
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = INFO
+formatter = generic
+
+[formatter_generic]
+format = %(asctime)s %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %Y-%m-%dT%H:%M:%S%z