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/url_mask_test.go

@@ -2,7 +2,6 @@ package delivery_test
 
 import (
 	"context"
-	"encoding/json"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -71,13 +70,6 @@ func deliverSlackTo(
 	e := testEngine(t, 1)
 	targetID := uuid.New().String()
 
-	slackCfg, err := json.Marshal(
-		delivery.SlackTargetConfig{
-			WebhookURL: webhookURL,
-		},
-	)
-	require.NoError(t, err)
-
 	event := seedEvent(t, db, `{"test":true}`)
 
 	dlv := seedDelivery(
@@ -87,7 +79,7 @@ func deliverSlackTo(
 
 	d := buildSlackDelivery(
 		dlv, event, targetID,
-		"test-slack-mask", string(slackCfg),
+		"test-slack-mask", webhookURL,
 	)
 
 	e.ExportDeliverSlack(context.TODO(), db, d)
@@ -160,13 +152,9 @@ func TestDoHTTPRequest_TransportErrorMasksURL(t *testing.T) {
 
 	e := testEngine(t, 1)
 
-	cfg, err := e.ExportParseHTTPConfig(
-		newHTTPTargetConfig(host + maskSecretPath),
-	)
-	require.NoError(t, err)
-
 	statusCode, _, _, reqErr := e.ExportDoHTTPRequest(
-		context.TODO(), cfg,
+		context.TODO(),
+		&database.Target{URL: host + maskSecretPath},
 		&database.Event{Body: `{"test":true}`},
 	)
 	require.Error(t, reqErr)
@@ -188,7 +176,7 @@ func TestDoHTTPRequest_UnparsableURLIsMasked(t *testing.T) {
 
 	statusCode, _, _, reqErr := e.ExportDoHTTPRequest(
 		context.TODO(),
-		&delivery.HTTPTargetConfig{
+		&database.Target{
 			URL: "https://hooks.example.com" + maskSecretPath + "\n",
 		},
 		&database.Event{},