Show each entrypoint's last event and event count on the webhook page (closes #393)

The entrypoint list showed no sign of whether anything uses an entrypoint, so an operator with several could not tell which senders are live before deactivating or deleting one. Each entrypoint now shows when its last event arrived, relative with the UTC time on hover, or "never", and how many events arrived through it within the webhook's retention. The last-event time comes from a new entrypoint_totals row written in the transaction that stores the event and left by retention, so a sender quieter than the retention period does not read "never". The count is one grouped query over a new index. Resubmitted copies count in neither. Pre-1.0: schema changed in place.

Model: opus-5-5

internal/database/model_totals.go

@@ -52,6 +52,21 @@ func (TargetTotals) TableName() string {
 	return "target_totals"
 }
 
+// EntrypointTotals is one row per entrypoint, created by the first
+// event that arrives on its URL: when the newest such event arrived,
+// which retention leaves as it is. A resubmitted copy did not arrive
+// on the URL and does not change it.
+type EntrypointTotals struct {
+	EntrypointID string `gorm:"type:uuid;primaryKey"`
+
+	LastEventAt time.Time `gorm:"not null"`
+}
+
+// TableName names the table AddEntrypointTotals updates.
+func (EntrypointTotals) TableName() string {
+	return "entrypoint_totals"
+}
+
 // AddEventTotals adds each count in add to the webhook's event totals,
 // and records add.LastEventAt as when the newest event arrived if it is
 // set. Call it on the transaction that writes or deletes the events it
@@ -97,3 +112,25 @@ func AddTargetTotals(tx *gorm.DB, add TargetTotals) error {
 
 	return nil
 }
+
+// AddEntrypointTotals records add.LastEventAt as when the newest event
+// arrived on the URL of the entrypoint add.EntrypointID names, creating
+// its row the first time. Call it on the transaction that stores the
+// event.
+func AddEntrypointTotals(tx *gorm.DB, add EntrypointTotals) error {
+	err := tx.Exec(
+		`INSERT INTO entrypoint_totals (entrypoint_id, last_event_at)
+		VALUES (?, ?)
+		ON CONFLICT (entrypoint_id) DO UPDATE SET
+			last_event_at = excluded.last_event_at`,
+		add.EntrypointID, add.LastEventAt,
+	).Error
+	if err != nil {
+		return fmt.Errorf(
+			"adding to totals of entrypoint %s: %w",
+			add.EntrypointID, err,
+		)
+	}
+
+	return nil
+}