feat(tests): add live subprocess integration test suite for services

Spins up each service's server.py in a real subprocess via a free ephemeral
port (PORT env var), connects with real protocol clients, and asserts both
correct protocol behavior and RFC 5424 log output.

- 44 live tests across 10 services: http, ftp, smtp, redis, mqtt,
  mysql, postgres, mongodb, pop3, imap
- Shared conftest.py: _ServiceProcess (bg reader thread + queue),
  free_port, live_service fixture, assert_rfc5424 helper
- PORT env var added to all 10 targeted server.py templates
- New pytest marker `live`; excluded from default addopts run
- requirements-live-tests.txt: flask, twisted + protocol clients

tests/live/test_mongodb_live.py

@@ -0,0 +1,70 @@
+import pytest
+import pymongo
+
+from tests.live.conftest import assert_rfc5424
+
+
+@pytest.mark.live
+class TestMongoDBLive:
+    def test_connect_succeeds(self, live_service):
+        port, drain = live_service("mongodb")
+        client = pymongo.MongoClient(
+            f"mongodb://127.0.0.1:{port}/",
+            serverSelectionTimeoutMS=5000,
+            connectTimeoutMS=5000,
+        )
+        # ismaster is handled — should not raise
+        client.admin.command("ismaster")
+        client.close()
+
+    def test_connect_logged(self, live_service):
+        port, drain = live_service("mongodb")
+        client = pymongo.MongoClient(
+            f"mongodb://127.0.0.1:{port}/",
+            serverSelectionTimeoutMS=5000,
+            connectTimeoutMS=5000,
+        )
+        try:
+            client.admin.command("ismaster")
+        except Exception:
+            pass
+        finally:
+            client.close()
+        lines = drain()
+        assert_rfc5424(lines, service="mongodb", event_type="connect")
+
+    def test_message_logged(self, live_service):
+        port, drain = live_service("mongodb")
+        client = pymongo.MongoClient(
+            f"mongodb://127.0.0.1:{port}/",
+            serverSelectionTimeoutMS=5000,
+            connectTimeoutMS=5000,
+        )
+        try:
+            client.admin.command("ismaster")
+        except Exception:
+            pass
+        finally:
+            client.close()
+        lines = drain()
+        assert_rfc5424(lines, service="mongodb", event_type="message")
+
+    def test_list_databases(self, live_service):
+        port, drain = live_service("mongodb")
+        client = pymongo.MongoClient(
+            f"mongodb://127.0.0.1:{port}/",
+            serverSelectionTimeoutMS=5000,
+            connectTimeoutMS=5000,
+        )
+        try:
+            # list_database_names triggers OP_MSG
+            client.list_database_names()
+        except Exception:
+            pass
+        finally:
+            client.close()
+        lines = drain()
+        # At least one message was exchanged
+        assert any("mongodb" in l for l in lines), (
+            "Expected at least one mongodb log line"
+        )