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, so nothing that reads a target parses
it. 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.

Model: opus-5-5

internal/handlers/webhook.go

@@ -425,21 +425,26 @@ func buildDeliveryTasks(
 		}
 
 		tasks = append(tasks, delivery.Task{
-			DeliveryID:   dlv.ID,
-			EventID:      event.ID,
-			WebhookID:    event.WebhookID,
-			EntrypointID: event.EntrypointID,
-			TargetID:     targets[i].ID,
-			TargetName:   targets[i].Name,
-			TargetType:   targets[i].Type,
-			TargetConfig: targets[i].Config,
-			MaxAttempts:  targets[i].MaxAttempts,
-			Method:       event.Method,
-			RawQuery:     event.RawQuery,
-			Headers:      event.Headers,
-			ContentType:  event.ContentType,
-			Body:         bodyPtr,
-			AttemptNum:   1,
+			DeliveryID:      dlv.ID,
+			EventID:         event.ID,
+			WebhookID:       event.WebhookID,
+			EntrypointID:    event.EntrypointID,
+			TargetID:        targets[i].ID,
+			TargetName:      targets[i].Name,
+			TargetType:      targets[i].Type,
+			TargetURL:       targets[i].URL,
+			TargetHeaders:   targets[i].Headers,
+			TimeoutSeconds:  targets[i].TimeoutSeconds,
+			ForwardQuery:    targets[i].ForwardQuery,
+			ArchiveExpiry:   targets[i].ArchiveExpiry,
+			ArchiveRotation: targets[i].ArchiveRotation,
+			MaxAttempts:     targets[i].MaxAttempts,
+			Method:          event.Method,
+			RawQuery:        event.RawQuery,
+			Headers:         event.Headers,
+			ContentType:     event.ContentType,
+			Body:            bodyPtr,
+			AttemptNum:      1,
 		})
 	}