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

Each entrypoint in the webhook page's entrypoint list shows when the last event arrived on its URL (relative, with the full UTC time on hover), or "never" if none ever has, and how many events arrived on it within the webhook's retention period. The last event is kept per entrypoint in a new EntrypointTotals row in the event database, written in the transaction that stores the event, so retention leaves it in place. The count is one query per page, grouped by entrypoint, over a new events index on entrypoint_id, deleted_at, resubmitted_from_id and created_at. Resubmitted copies did not arrive on the URL and count in neither. Pre-1.0: the table and index go into the schema in place.

Model: opus-5-5

internal/database/webhook_db_manager.go

@@ -49,7 +49,7 @@ var ErrSidecarNotRemoved = errors.New(
 // WebhookDBManager manages per-webhook SQLite database files
 // for event storage. Each webhook gets its own dedicated
 // database containing Events, Deliveries, DeliveryResults and the
-// running totals of them (EventTotals, TargetTotals).
+// running totals of them (EventTotals, TargetTotals, EntrypointTotals).
 // Database connections are opened lazily and cached.
 type WebhookDBManager struct {
 	dataDir string
@@ -381,7 +381,7 @@ func (m *WebhookDBManager) openDB(
 	// Run migrations for event-tier models only
 	err = db.AutoMigrate(
 		&Event{}, &Delivery{}, &DeliveryResult{},
-		&EventTotals{}, &TargetTotals{},
+		&EventTotals{}, &TargetTotals{}, &EntrypointTotals{},
 	)
 	if err != nil {
 		_ = sqlDB.Close()