feat: add pipeline busy status indicator with breathing effect

- Add pipeline_busy field to health check response
- Track pipeline busy state in frontend store
- Add breathing animation for pipeline status button
- Enhance dark mode visibility with stronger contrast

lightrag_webui/src/api/lightrag.ts

@@ -45,6 +45,7 @@ export type LightragStatus = {
   core_version?: string
   api_version?: string
   auth_mode?: 'enabled' | 'disabled'
+  pipeline_busy: boolean
 }
 
 export type LightragDocumentsScanProgress = {