feat(argocd): recover Telegram notifications (failed/degraded) and prune for polymarket-bot

- Notifications via generic webhook to the Telegram Bot API: the engine's
  native telegram service only supports channels and negative group IDs,
  so a positive private chat_id never worked ("chat not found").
- Only on-sync-failed and on-health-degraded triggers; on-sync-succeeded
  dropped (CI already reports successful deploys).
- Subscribe annotations on polymarket-bot, researchowl and n8n.
- prune: true on polymarket-bot, guarded by Prune=false on the postgres
  PVC so removing the manifest from git can never destroy the data.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

polymarket-bot/pvc-data-postgres-0.yaml

@@ -2,6 +2,8 @@ apiVersion: v1
 kind: PersistentVolumeClaim
 metadata:
   annotations:
+    # Never let ArgoCD prune this PVC: it holds the paper-trading postgres data.
+    argocd.argoproj.io/sync-options: Prune=false
     pv.kubernetes.io/bind-completed: 'yes'
     pv.kubernetes.io/bound-by-controller: 'yes'
     volume.beta.kubernetes.io/storage-provisioner: rancher.io/local-path