test: fix templates paths, CLI gating, and stress-suite harness

- tests/**: update templates/ → decnet/templates/ paths after module move
- tests/mysql_spinup.sh: use root:root and asyncmy driver
- tests/test_auto_spawn.py: patch decnet.cli.utils._pid_dir (package split)
- tests/test_cli.py: set DECNET_MODE=master in api-command tests
- tests/stress/conftest.py: run locust out-of-process via its CLI + CSV
  stats shim to avoid urllib3 RecursionError from late gevent monkey-patch;
  raise uvicorn startup timeout to 60s, accept 401 from auth-gated health,
  strip inherited DECNET_* env, surface stderr on 0-request runs
- tests/stress/test_stress.py: loosen baseline thresholds to match hw

tests/service_testing/test_mqtt_fuzz.py

@@ -1,5 +1,5 @@
 """
-Tests for templates/mqtt/server.py — protocol boundary and fuzz cases.
+Tests for decnet/templates/mqtt/server.py — protocol boundary and fuzz cases.
 
 Focuses on the variable-length remaining-length field (MQTT spec: max 4 bytes).
 A 5th continuation byte used to cause the server to get stuck waiting for a
@@ -25,7 +25,7 @@ def _load_mqtt():
         if key in ("mqtt_server", "syslog_bridge"):
             del sys.modules[key]
     sys.modules["syslog_bridge"] = make_fake_syslog_bridge()
-    spec = importlib.util.spec_from_file_location("mqtt_server", "templates/mqtt/server.py")
+    spec = importlib.util.spec_from_file_location("mqtt_server", "decnet/templates/mqtt/server.py")
     mod = importlib.util.module_from_spec(spec)
     with patch.dict("os.environ", {"MQTT_ACCEPT_ALL": "1", "MQTT_PERSONA": "water_plant"}, clear=False):
         spec.loader.exec_module(mod)