SIENTIAPDE-2202

SIENTIAPDE-2202 Add gateway end-to-end test suite (e2e/)

End-to-end suite at the repo root, following the Laborious/Orchestrator
pattern: numbered scenarios per topic in e2e/scenarios.md (1:1 with
test_scenario_* functions), scenario inputs as JSON, Postgres DDL mirrored
from production, `integration` marker, excluded from the default pytest run.

Every dependency runs for real: MongoDB, Redis, PostgreSQL, MinIO and NATS
via testcontainers, OPC UA servers in process (asyncua). Pods are built from
the environment like ingestor/app.py and driven one loop iteration at a time.

69 scenarios across 7 topics: slot leasing and failover, subscription reads,
NATS writes and write_status (incl. the SIENTIAPDE-2202 timestamp/quality
matrix, checked on the server and on the wire), gRPC ReadTag, active reads,
client certificates/security, pod lifecycle.

Replaces tests/functional (legacy slot v1 tests, fully commented out) and
tests/functional/test_write_e2e.py (now scenarios 3.1.x).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

e2e/scenario_inputs/write_command.json

@@ -0,0 +1,12 @@
+{
+  "server_id": "1",
+  "addr": "ns=2;s=Setpoint",
+  "value": 1.25,
+  "data_type": "float",
+  "tag_type": "prediction",
+  "model_id": "2",
+  "model_name": "sin-approx",
+  "schema": "sientia_data",
+  "table_name": "predictions",
+  "timestamp": "2026-10-13T12:00:00-03:00"
+}