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/export_test.go

@@ -77,10 +77,10 @@ func ExportIsForwardableHeader(name string) bool {
 func ExportApplyRequestHeaders(
 	req *http.Request,
 	event *database.Event,
-	cfg *HTTPTargetConfig,
+	configured map[string]string,
 	userAgent string,
 ) []string {
-	return applyRequestHeaders(req, event, cfg, userAgent)
+	return applyRequestHeaders(req, event, configured, userAgent)
 }
 
 // ExportTruncate exposes truncate for testing.
@@ -216,37 +216,23 @@ func (e *Engine) ExportSetSlackCircuitBreaker(
 	e.slackTarget.circuitBreakers.Store(targetID, cb)
 }
 
-// ExportParseHTTPConfig exposes parseHTTPConfig.
-func (e *Engine) ExportParseHTTPConfig(
-	configJSON string,
-) (*HTTPTargetConfig, error) {
-	return parseHTTPConfig(configJSON)
-}
-
-// ExportParseSlackConfig exposes parseSlackConfig.
-func (e *Engine) ExportParseSlackConfig(
-	configJSON string,
-) (*SlackTargetConfig, error) {
-	return parseSlackConfig(configJSON)
-}
-
 // ExportDoHTTPRequest exposes the http target's
 // doHTTPRequest.
 func (e *Engine) ExportDoHTTPRequest(
 	ctx context.Context,
-	cfg *HTTPTargetConfig,
+	target *database.Target,
 	event *database.Event,
 ) (int, string, int64, error) {
-	return e.httpTarget.doHTTPRequest(ctx, cfg, event)
+	return e.httpTarget.doHTTPRequest(ctx, target, event)
 }
 
 // ExportClientForRequest exposes the http target's
 // clientForRequest.
 func (e *Engine) ExportClientForRequest(
-	cfg *HTTPTargetConfig,
+	timeoutSeconds int,
 	originScoped []string,
 ) *http.Client {
-	return e.httpTarget.clientForRequest(cfg, originScoped)
+	return e.httpTarget.clientForRequest(timeoutSeconds, originScoped)
 }
 
 // ErrExportTooManyRedirects exposes the sentinel the redirect