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/export_test.go

@@ -133,36 +133,28 @@ func (s *Handlers) RenderTemplateForTest(
 	s.renderTemplate(w, r, pageTemplate, data)
 }
 
-// BuildSlackTargetConfigForTest exposes
-// buildSlackTargetConfig for use in the handlers_test package.
-func (s *Handlers) BuildSlackTargetConfigForTest(
+// SetSlackTargetSettingsForTest exposes setSlackTargetSettings for use
+// in the handlers_test package.
+func (s *Handlers) SetSlackTargetSettingsForTest(
 	ctx context.Context,
+	target *database.Target,
 	targetURL string,
-) (string, string, error) {
-	return s.buildSlackTargetConfig(ctx, targetURL)
+) string {
+	return s.setSlackTargetSettings(ctx, target, targetURL)
 }
 
-// BuildHTTPTargetConfigForTest exposes buildHTTPTargetConfig
-// for use in the handlers_test package, taking the form fields
-// an HTTP target's configuration is built from.
-func (s *Handlers) BuildHTTPTargetConfigForTest(
-	ctx context.Context,
-	targetURL, headers, timeout string,
-) (string, string, error) {
-	return s.buildHTTPTargetConfig(ctx, targetFormInput{
-		URL:     targetURL,
-		Headers: headers,
-		Timeout: timeout,
-	})
-}
-
-// BuildDatabaseTargetConfigForTest exposes
-// buildDatabaseTargetConfig for use in the handlers_test
-// package.
-func BuildDatabaseTargetConfigForTest(
+// SetDatabaseTargetSettingsForTest exposes setDatabaseTargetSettings
+// for use in the handlers_test package.
+func SetDatabaseTargetSettingsForTest(
+	target *database.Target,
 	expiry, rotation string,
-) (string, string, error) {
-	return buildDatabaseTargetConfig(expiry, rotation)
+) string {
+	return setDatabaseTargetSettings(target, expiry, rotation)
+}
+
+// FormatArchiveExpiryForTest exposes formatArchiveExpiry.
+func FormatArchiveExpiryForTest(expiry time.Duration) string {
+	return formatArchiveExpiry(expiry)
 }
 
 // ArchiveFileViewForTest exposes archiveFileView, which describes a