Fix two resubmit comments and test the resubmit route's middleware (closes #252)

loadResubmitSource credited GORM's soft-delete scope for refusing a
reaped event; the reaper deletes the row outright. createAndFanOut
claimed to be the only path that creates deliveries; per-delivery
replay creates one too.

New tests drive the resubmit route through the production router:
CSRF refuses a missing, malformed or foreign token; another user's
webhook and another webhook's event are 404; the rate limit refuses
once spent; and signed-out requests never reach that rate limit. The
handler refuses a signed-out request with the same redirect itself,
so keeping such requests off the budget is what RequireAuth adds.

Model: opus-5-5

internal/server/routes_test.go

@@ -444,6 +444,23 @@ func (e *testEnv) countDeliveries(
 	return count
 }
 
+// countEvents reports how many events a webhook's database holds.
+func (e *testEnv) countEvents(t *testing.T, webhookID string) int64 {
+	t.Helper()
+
+	webhookDB, err := e.dbMgr.GetDB(webhookID)
+	require.NoError(t, err)
+
+	var count int64
+
+	require.NoError(
+		t,
+		webhookDB.Model(&database.Event{}).Count(&count).Error,
+	)
+
+	return count
+}
+
 // storedHash reads the current password hash for a username.
 func (e *testEnv) storedHash(t *testing.T, username string) string {
 	t.Helper()