fix(updater): fall back to /proc scan when agent.pid is missing

If the agent was started outside the updater (manually, during dev,
or from a prior systemd unit), there is no agent.pid for _stop_agent
to target, so a successful code install leaves the old in-memory
agent process still serving requests. Scan /proc for any decnet agent
command and SIGTERM all matches so restart is reliable regardless of
how the agent was originally launched.

pyproject.toml

@@ -25,7 +25,9 @@ dependencies = [
     "scapy>=2.6.1",
     "orjson>=3.10",
     "cryptography>=46.0.7",
-    "python-multipart>=0.0.20"
+    "python-multipart>=0.0.20",
+    "httpx>=0.28.1",
+    "requests>=2.33.1"
 ]
 
 [project.optional-dependencies]