Store a target's number of delivery attempts, at least one (closes #540)

Target.MaxRetries (max_retries) becomes Target.MaxAttempts
(max_attempts), and the form field, parser and ceiling are renamed to
match. 1 is a single attempt with no circuit breaker; above 1 retries
behind the breaker up to that many attempts. Both target forms refuse
0 and less and default a blank field to 1. The target page shows the
plain number, and the README's two paragraphs on 0 against 1 become
one sentence.

Model: opus-5-5

internal/handlers/target_create_test.go

@@ -21,24 +21,24 @@ func TestHandleTargetCreate_EveryType(t *testing.T) {
 
 	// fields is the rest of each submission, as a query string.
 	cases := []struct {
-		targetType  database.TargetType
-		fields      string
-		wantConfig  string
-		wantRetries int
+		targetType   database.TargetType
+		fields       string
+		wantConfig   string
+		wantAttempts int
 	}{
 		{
-			database.TargetTypeHTTP, "timeout=12&max_retries=3",
+			database.TargetTypeHTTP, "timeout=12&max_attempts=3",
 			`{"url":"` + editOriginalURL + `","timeout":12}`, 3,
 		},
 		{
-			database.TargetTypeSlack, "max_retries=4",
+			database.TargetTypeSlack, "max_attempts=4",
 			`{"webhookUrl":"` + editOriginalURL + `"}`, 4,
 		},
 		{
 			database.TargetTypeDatabase, "expiry=720h",
-			`{"expiry":"720h"}`, 0,
+			`{"expiry":"720h"}`, 1,
 		},
-		{database.TargetTypeLog, "", "", 0},
+		{database.TargetTypeLog, "", "", 1},
 	}
 
 	for _, tc := range cases {
@@ -62,7 +62,7 @@ func TestHandleTargetCreate_EveryType(t *testing.T) {
 			targets := targetsForWebhook(t, env.db, webhook.ID)
 			require.Len(t, targets, 1)
 			assert.Equal(t, tc.targetType, targets[0].Type)
-			assert.Equal(t, tc.wantRetries, targets[0].MaxRetries)
+			assert.Equal(t, tc.wantAttempts, targets[0].MaxAttempts)
 
 			if tc.wantConfig == "" {
 				assert.Empty(t, targets[0].Config)
@@ -90,11 +90,11 @@ func TestHandleTargetCreate_RefusedFormComesBack(t *testing.T) {
 		{
 			database.TargetTypeHTTP,
 			"name=private&url=" + editBlockedURL +
-				"&timeout=12&max_retries=3",
+				"&timeout=12&max_attempts=3",
 			"Invalid target URL",
 		},
 		{
-			database.TargetTypeSlack, "name=no-url&max_retries=4",
+			database.TargetTypeSlack, "name=no-url&max_attempts=4",
 			"Webhook URL is required for Slack targets",
 		},
 		{
@@ -133,8 +133,8 @@ func TestHandleTargetCreate_RefusedFormComesBack(t *testing.T) {
 			assert.Contains(t, page, html.EscapeString(tc.reason))
 
 			// Each value comes back in a data attribute of the targets
-			// section named after its field (max_retries as
-			// data-max-retries), except url, which comes back in
+			// section named after its field (max_attempts as
+			// data-max-attempts), except url, which comes back in
 			// data-destination; templates/source_detail.html says why.
 			for field := range typed {
 				attr := "data-" + strings.ReplaceAll(field, "_", "-")