Fix XID Age graph to show threshold context

- Add fixed Y-axis (0-220M) so the autovacuum threshold is always visible
- Add dashed threshold lines at 150M (yellow) and 200M (red)
- Update title to mention the 200M threshold

The raw XID age will always trend upward between vacuum freezes,
which looked alarming without context. Now the graph shows how
far the value is from the autovacuum_freeze_max_age threshold.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

argocd/manifests/grafana-config/dashboards/configmap-postgresql.yaml

@@ -534,13 +534,19 @@ data:
                   "mode": "none"
                 },
                 "thresholdsStyle": {
-                  "mode": "off"
+                  "mode": "dashed"
                 }
               },
               "mappings": [],
+              "max": 220000000,
+              "min": 0,
               "thresholds": {
                 "mode": "absolute",
-                "steps": [{ "color": "green", "value": null }]
+                "steps": [
+                  { "color": "green", "value": null },
+                  { "color": "yellow", "value": 150000000 },
+                  { "color": "red", "value": 200000000 }
+                ]
               },
               "unit": "short"
             }
@@ -566,7 +572,7 @@ data:
               "refId": "A"
             }
           ],
-          "title": "XID Age Over Time",
+          "title": "Tesla XID Age (autovacuum threshold: 200M)",
           "type": "timeseries"
         }
       ],