fix(hermesagent): add external script warning and remove redundant check

Adds third-party script warning with user confirmation before running
the upstream installer (install) and updater (update), matching the
kasm/pihole pattern. Removes redundant binary existence check per
reviewer feedback. Adds corresponding JSON warning note.

json/hermesagent.json

@@ -32,6 +32,10 @@
         "password": null
     },
     "notes": [
+        {
+            "text": "WARNING: Installation sources scripts outside of Community Scripts repo. Please check the source before installing.",
+            "type": "warning"
+        },
         {
             "text": "Warning: Hermes can execute terminal commands. The agent runs as a dedicated 'hermes' service user for isolation.",
             "type": "warning"