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/delivery/event_timestamp_test.go

@@ -93,17 +93,6 @@ func (s *tsSink) text(t *testing.T) string {
 	}
 }
 
-func tsSlackConfig(t *testing.T, url string) string {
-	t.Helper()
-
-	data, err := json.Marshal(
-		delivery.SlackTargetConfig{WebhookURL: url},
-	)
-	require.NoError(t, err)
-
-	return string(data)
-}
-
 // tsSeedEvent writes an event whose CreatedAt is tsEventCreatedAt
 // rather than the write time, so an assertion on the rendered
 // timestamp cannot pass by accident against "roughly now".
@@ -142,7 +131,7 @@ func tsSeedEvent(
 // tsSeedTarget writes the slack target row into the main database.
 // The retry path confirms the target still exists before sending.
 func tsSeedTarget(
-	t *testing.T, mainDB *gorm.DB, webhookID, config string,
+	t *testing.T, mainDB *gorm.DB, webhookID, webhookURL string,
 ) database.Target {
 	t.Helper()
 
@@ -150,7 +139,7 @@ func tsSeedTarget(
 		WebhookID:   webhookID,
 		Name:        "slack-sink",
 		Type:        database.TargetTypeSlack,
-		Config:      config,
+		URL:         webhookURL,
 		Active:      true,
 		MaxAttempts: 1,
 	}
@@ -176,7 +165,7 @@ func tsTask(
 		TargetID:     target.ID,
 		TargetName:   target.Name,
 		TargetType:   database.TargetTypeSlack,
-		TargetConfig: target.Config,
+		TargetURL:    target.URL,
 		MaxAttempts:  1,
 		Method:       event.Method,
 		Headers:      event.Headers,
@@ -226,8 +215,7 @@ func (c tsCase) run(t *testing.T) (iSetup, database.Delivery, string) {
 	s := newISetup(t)
 	sink := newTSSink(t)
 
-	cfg := tsSlackConfig(t, sink.URL)
-	target := tsSeedTarget(t, s.MainDB, s.WebhookID, cfg)
+	target := tsSeedTarget(t, s.MainDB, s.WebhookID, sink.URL)
 	event := tsSeedEvent(t, s.WebhookDB, s.WebhookID)
 
 	d := iSeedDelivery(
@@ -338,8 +326,7 @@ func TestFormatSlackMessageOverTaskReconstructedEvent(
 
 	s := newISetup(t)
 
-	cfg := tsSlackConfig(t, tsUndeliverableHook)
-	target := tsSeedTarget(t, s.MainDB, s.WebhookID, cfg)
+	target := tsSeedTarget(t, s.MainDB, s.WebhookID, tsUndeliverableHook)
 	event := tsSeedEvent(t, s.WebhookDB, s.WebhookID)
 
 	d := iSeedDelivery(
@@ -410,8 +397,7 @@ func TestEventReconstructionSurvivesAReapedRow(t *testing.T) {
 
 	s := newISetup(t)
 
-	cfg := tsSlackConfig(t, tsUndeliverableHook)
-	target := tsSeedTarget(t, s.MainDB, s.WebhookID, cfg)
+	target := tsSeedTarget(t, s.MainDB, s.WebhookID, tsUndeliverableHook)
 	event := tsSeedEvent(t, s.WebhookDB, s.WebhookID)
 
 	d := iSeedDelivery(