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/archive/archive.go

@@ -143,26 +143,15 @@ func archiveNamePart(name string) string {
 }
 
 // Write writes the full event of a delivery to a database target as
-// a row into the target's archive database, honouring the optional
-// per-target expiry and rotation parsed from the target config JSON.
-// With rotation, the event goes to the file for the period of its
-// receive time.
+// a row into the target's archive database, honouring the target's
+// ArchiveExpiry and ArchiveRotation. With rotation, the event goes to
+// the file for the period of its receive time.
 func (ws *Writers) Write(d *database.Delivery) error {
 	webhookID := d.Event.WebhookID
 	if webhookID == "" {
 		return errArchiveMissingWebhookID
 	}
 
-	expiry, err := ParseExpiry(d.Target.Config)
-	if err != nil {
-		return err
-	}
-
-	rotation, err := ParseRotation(d.Target.Config)
-	if err != nil {
-		return err
-	}
-
 	// An event whose stored row was gone before its delivery ran has
 	// no receive time (see delivery's Engine.hydrateEvent), and goes
 	// to the file for now.
@@ -187,7 +176,10 @@ func (ws *Writers) Write(d *database.Delivery) error {
 		ContentType:  d.Event.ContentType,
 	}
 
-	return w.write(row, expiry, archivePeriod(rotation, receivedAt))
+	return w.write(
+		row, d.Target.ArchiveExpiry,
+		archivePeriod(d.Target.ArchiveRotation, receivedAt),
+	)
 }
 
 // Rename implements Archives. It renames every one of a database