fix(agent-pod): pin pi-coding-agent to a version that actually exists on npm

0.1.23 was pi's own internal version string (from local pi --version),
not the npm package's semver -- npm has no such release, so the
container crash-looped on ETARGET. Latest published is 0.84.2.

k8s/apps/agent-pod/deployment.yaml

@@ -19,7 +19,7 @@ spec:
           command:
             - sh
             - -c
-            - "npm install -g @earendil-works/pi-coding-agent@0.1.23 && sleep infinity"
+            - "npm install -g @earendil-works/pi-coding-agent@0.84.2 && sleep infinity"
           resources:
             requests:
               cpu: "2"