The usage sums and exports count pictures

The five-minute, hourly and daily sums gain images (migration 0042), and
the CSV and JSON exports a column for them: once request rows were past
their retention, an export said what pictures cost but not how many there
were. The pictures made before are added to the sums from their rows.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/admin-api.openapi.json

@@ -10288,6 +10288,10 @@
           "CostMicros": {
             "type": "integer",
             "format": "int64"
+          },
+          "Images": {
+            "type": "integer",
+            "format": "int64"
           }
         }
       },