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/webhook_create.go

@@ -115,13 +115,7 @@ func (h *Handlers) HandleSourceCreateSubmit() http.HandlerFunc {
 			return
 		}
 
-		targets, errMsg, err := h.newWebhookTargets(r.Context(), in)
-		if err != nil {
-			h.serverError(w, r, "failed to encode target config", err)
-
-			return
-		}
-
+		targets, errMsg := h.newWebhookTargets(r.Context(), in)
 		if errMsg != "" {
 			refuse(errMsg)
 
@@ -147,7 +141,7 @@ func (h *Handlers) HandleSourceCreateSubmit() http.HandlerFunc {
 func (h *Handlers) newWebhookTargets(
 	ctx context.Context,
 	in sourceFormInput,
-) ([]*database.Target, string, error) {
+) ([]*database.Target, string) {
 	var requested []targetFormInput
 
 	if in.HTTPURL != "" {
@@ -170,15 +164,15 @@ func (h *Handlers) newWebhookTargets(
 	targets := make([]*database.Target, 0, len(requested))
 
 	for _, form := range requested {
-		target, errMsg, err := h.newTarget(ctx, "", form)
-		if err != nil || errMsg != "" {
-			return nil, errMsg, err
+		target, errMsg := h.newTarget(ctx, "", form)
+		if errMsg != "" {
+			return nil, errMsg
 		}
 
 		targets = append(targets, target)
 	}
 
-	return targets, "", nil
+	return targets, ""
 }
 
 // createWebhookWithEntrypoint creates a webhook, its default