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/handlers/delivery_replay.go

@@ -300,21 +300,26 @@ func createReplayDelivery(
 	}
 
 	return delivery.Task{
-		DeliveryID:   dlv.ID,
-		EventID:      event.ID,
-		WebhookID:    webhookID,
-		EntrypointID: event.EntrypointID,
-		TargetID:     target.ID,
-		TargetName:   target.Name,
-		TargetType:   target.Type,
-		TargetConfig: target.Config,
-		MaxAttempts:  target.MaxAttempts,
-		Method:       event.Method,
-		RawQuery:     event.RawQuery,
-		Headers:      event.Headers,
-		ContentType:  event.ContentType,
-		Body:         replayBody(event.Body),
-		AttemptNum:   1,
+		DeliveryID:      dlv.ID,
+		EventID:         event.ID,
+		WebhookID:       webhookID,
+		EntrypointID:    event.EntrypointID,
+		TargetID:        target.ID,
+		TargetName:      target.Name,
+		TargetType:      target.Type,
+		TargetURL:       target.URL,
+		TargetHeaders:   target.Headers,
+		TimeoutSeconds:  target.TimeoutSeconds,
+		ForwardQuery:    target.ForwardQuery,
+		ArchiveExpiry:   target.ArchiveExpiry,
+		ArchiveRotation: target.ArchiveRotation,
+		MaxAttempts:     target.MaxAttempts,
+		Method:          event.Method,
+		RawQuery:        event.RawQuery,
+		Headers:         event.Headers,
+		ContentType:     event.ContentType,
+		Body:            replayBody(event.Body),
+		AttemptNum:      1,
 	}, nil
 }