Store a target's settings as columns (closes #543)

A target's settings move from the per-type JSON string in
targets.config to columns: url, headers, timeout_seconds,
forward_query, archive_expiry and archive_rotation. A column a type
does not use stays empty. headers holds the header map as JSON text
through GORM's JSON serializer, and archive_expiry holds a
time.Duration, 0 meaning never. The forms check each setting once,
with the same refusals and messages, and the edit form is filled from
the columns, so the per-type config structs, their parsers and the
"could not be read" branches are gone. A delivery task carries the
six settings in place of the JSON string; tests check that each copy
into a task, and back out of one, keeps all six.

Model: opus-5-5

internal/delivery/metrics_test.go

@@ -192,7 +192,7 @@ func mDeliverOK(t *testing.T, s iSetup) {
 	body := event.Body
 	task := iTask(
 		d, event, s.WebhookID, targetID,
-		"metrics-ok", iHTTPConfig(ts.URL), 3, 1, &body,
+		"metrics-ok", ts.URL, 3, 1, &body,
 	)
 
 	s.Engine.ExportProcessNewTask(context.TODO(), &task)
@@ -226,18 +226,17 @@ func mExhaustRetries(t *testing.T, s iSetup) {
 	)
 
 	body := event.Body
-	cfg := iHTTPConfig(ts.URL)
 
 	// The retry below is only run if its target still exists; see
 	// https://git.eeqj.de/sneak/webhooker/issues/107.
 	iCreateTarget(
 		t, s.MainDB, targetID, s.WebhookID, "metrics-fail",
-		database.TargetTypeHTTP, cfg, 2,
+		database.TargetTypeHTTP, ts.URL, 2,
 	)
 
 	first := iTask(
 		d, event, s.WebhookID, targetID,
-		"metrics-fail", cfg, 2, 1, &body,
+		"metrics-fail", ts.URL, 2, 1, &body,
 	)
 
 	s.Engine.ExportProcessNewTask(context.TODO(), &first)
@@ -251,7 +250,7 @@ func mExhaustRetries(t *testing.T, s iSetup) {
 	// deterministic and off the wall clock.
 	second := iTask(
 		d, event, s.WebhookID, targetID,
-		"metrics-fail", cfg, 2, 2, &body,
+		"metrics-fail", ts.URL, 2, 2, &body,
 	)
 
 	s.Engine.ExportProcessRetryTask(
@@ -289,7 +288,6 @@ func TestDeliveryMetrics_CircuitBreakerGauge(t *testing.T) {
 	)
 
 	body := event.Body
-	cfg := iHTTPConfig(ts.URL)
 
 	// An attempt budget above the failure threshold, so the breaker
 	// rather than the budget is what stops the delivery.
@@ -299,12 +297,12 @@ func TestDeliveryMetrics_CircuitBreakerGauge(t *testing.T) {
 	// see https://git.eeqj.de/sneak/webhooker/issues/107.
 	iCreateTarget(
 		t, s.MainDB, targetID, s.WebhookID, "metrics-trip",
-		database.TargetTypeHTTP, cfg, maxAttempts,
+		database.TargetTypeHTTP, ts.URL, maxAttempts,
 	)
 
 	first := iTask(
 		d, event, s.WebhookID, targetID,
-		"metrics-trip", cfg, maxAttempts, 1, &body,
+		"metrics-trip", ts.URL, maxAttempts, 1, &body,
 	)
 
 	s.Engine.ExportProcessNewTask(context.TODO(), &first)
@@ -316,7 +314,7 @@ func TestDeliveryMetrics_CircuitBreakerGauge(t *testing.T) {
 		ExportDefaultFailureThreshold; attempt++ {
 		task := iTask(
 			d, event, s.WebhookID, targetID,
-			"metrics-trip", cfg, maxAttempts, attempt, &body,
+			"metrics-trip", ts.URL, maxAttempts, attempt, &body,
 		)
 
 		s.Engine.ExportProcessRetryTask(
@@ -363,17 +361,16 @@ func TestDeliveryMetrics_BreakerBlockedIsNotAnAttempt(
 	)
 
 	body := event.Body
-	cfg := iHTTPConfig(ts.URL)
 	maxAttempts := delivery.ExportDefaultFailureThreshold + 5
 
 	iCreateTarget(
 		t, s.MainDB, targetID, s.WebhookID, "metrics-blocked",
-		database.TargetTypeHTTP, cfg, maxAttempts,
+		database.TargetTypeHTTP, ts.URL, maxAttempts,
 	)
 
 	first := iTask(
 		d, event, s.WebhookID, targetID,
-		"metrics-blocked", cfg, maxAttempts, 1, &body,
+		"metrics-blocked", ts.URL, maxAttempts, 1, &body,
 	)
 
 	s.Engine.ExportProcessNewTask(context.TODO(), &first)
@@ -382,7 +379,7 @@ func TestDeliveryMetrics_BreakerBlockedIsNotAnAttempt(
 		ExportDefaultFailureThreshold; attempt++ {
 		task := iTask(
 			d, event, s.WebhookID, targetID,
-			"metrics-blocked", cfg, maxAttempts, attempt, &body,
+			"metrics-blocked", ts.URL, maxAttempts, attempt, &body,
 		)
 
 		s.Engine.ExportProcessRetryTask(context.TODO(), &task)
@@ -405,7 +402,7 @@ func TestDeliveryMetrics_BreakerBlockedIsNotAnAttempt(
 
 	blocked := iTask(
 		d, event, s.WebhookID, targetID,
-		"metrics-blocked", cfg, maxAttempts,
+		"metrics-blocked", ts.URL, maxAttempts,
 		delivery.ExportDefaultFailureThreshold+1, &body,
 	)
 
@@ -474,7 +471,7 @@ func TestDeliveryMetrics_QueueDepthGauges(t *testing.T) {
 
 	iCreateTarget(t, s.MainDB, targetID, s.WebhookID,
 		"queue-depth-target", database.TargetTypeHTTP,
-		iHTTPConfig("https://example.com/hook"), 3,
+		"https://example.com/hook", 3,
 	)
 
 	event := iSeedEvent(