refactor(tests): move flat tests/*.py into per-subsystem subfolders

Groups every flat test_*.py under the module it exercises, matching the
existing tests/{profiler,sniffer,prober,collector,correlation,cli,web,
topology,swarm,bus,updater,api,docker,geoip,...} layout. New folders:
services/, fleet/, config/, logging/, db/ (+ db/mysql/), telemetry/,
mutator/, core/.

Path-dependent __file__ references bumped an extra .parent in three
files that moved one level deeper:
- tests/sniffer/test_sniffer_ja3.py   (template path)
- tests/services/test_ssh_capture_emit.py (template path)
- tests/cli/test_mode_gating.py  (REPO root)
- tests/web/test_env_lazy_jwt.py (repo var)

Also drops two SQLite runtime artifacts (test_decnet.db-{shm,wal}) that
were leaking into the repo from a previous test run.

Fixes two test_service_isolation cases that patched asyncio.sleep (no
longer on the profiler main-loop hot path — same pre-existing bug I
fixed earlier in test_attacker_worker.py) by patching asyncio.wait_for
and passing interval=0.

tests/core/test_build.py

@@ -0,0 +1,66 @@
+"""Smoke test: verify the package and all submodules import cleanly."""
+import importlib
+import pytest
+
+
+MODULES = [
+    "decnet",
+    "decnet.cli",
+    "decnet.config",
+    "decnet.composer",
+    "decnet.engine",
+    "decnet.engine.deployer",
+    "decnet.collector",
+    "decnet.collector.worker",
+    "decnet.mutator",
+    "decnet.mutator.engine",
+    "decnet.fleet",
+    "decnet.network",
+    "decnet.archetypes",
+    "decnet.distros",
+    "decnet.os_fingerprint",
+    "decnet.ini_loader",
+    "decnet.custom_service",
+    "decnet.correlation",
+    "decnet.correlation.engine",
+    "decnet.correlation.graph",
+    "decnet.correlation.parser",
+    "decnet.logging",
+    "decnet.logging.file_handler",
+    "decnet.logging.forwarder",
+    "decnet.logging.syslog_formatter",
+    "decnet.services",
+    "decnet.services.registry",
+    "decnet.services.base",
+    "decnet.services.ssh",
+    "decnet.services.ftp",
+    "decnet.services.http",
+    "decnet.services.smb",
+    "decnet.services.rdp",
+    "decnet.services.smtp",
+    "decnet.services.mysql",
+    "decnet.services.postgres",
+    "decnet.services.redis",
+    "decnet.services.mongodb",
+    "decnet.services.mssql",
+    "decnet.services.elasticsearch",
+    "decnet.services.ldap",
+    "decnet.services.k8s",
+    "decnet.services.docker_api",
+    "decnet.services.vnc",
+    "decnet.services.telnet",
+    "decnet.services.tftp",
+    "decnet.services.snmp",
+    "decnet.services.sip",
+    "decnet.services.mqtt",
+    "decnet.services.llmnr",
+    "decnet.services.imap",
+    "decnet.services.pop3",
+    "decnet.services.conpot",
+    "decnet.services.registry",
+]
+
+
+@pytest.mark.parametrize("module", MODULES)
+def test_module_imports(module):
+    importlib.import_module(module)