fix(myorg-assistant): inject WEB_SECRET_KEY into all cronjobs

CronJob containers import src.config.Settings() at startup, which requires
WEB_SECRET_KEY. Only the Deployment set it; the 5 CronJobs (git-sync,
morning-briefing, evening-summary, waiting-followup, deadline-checker) crashed
at import with a pydantic ValidationError, causing restart loops (e.g.
myorg-git-sync ~5 restarts/15m). Pull WEB_SECRET_KEY from the existing
myorg-assistant-secret so the cronjobs start cleanly.

myorg-assistant/cronjobs/deadline-checker.yaml

@@ -54,6 +54,11 @@ spec:
                 secretKeyRef:
                   name: myorg-assistant-secret
                   key: LITELLM_API_KEY
+            - name: WEB_SECRET_KEY
+              valueFrom:
+                secretKeyRef:
+                  name: myorg-assistant-secret
+                  key: WEB_SECRET_KEY
             volumeMounts:
             - name: myorg-data
               mountPath: /data/myorg