release: 1.5.0: Send-log retention configurable in panel Settings

Send-log retention is configurable from panel **Settings** (global administrator); `SEND_LOG_RETENTION_DAYS` seeds the initial default only.
Added:
  - Panel **Settings** (global administrator): **Send log retention (days)** —
Changed:
  - Deliveries list and delivery detail pages show the configured retention

Full detail: CHANGELOG.md (1.5.0).

internal/web/handlers/handlers.go

@@ -38,6 +38,9 @@ type Config struct {
 	// InboundEnabled mirrors INBOUND_RELAY_ENABLE: the inbound panel and
 	// routes exist only when this is true.
 	InboundEnabled bool
+	// SendLogRetentionEnvDefault is SEND_LOG_RETENTION_DAYS at panel start; used
+	// as bootstrap and fallback when the settings row is missing or invalid.
+	SendLogRetentionEnvDefault int
 }
 
 // Handlers holds dependencies for authenticated panel routes.