fix: prevent install buttons showing before first container scan

Added containers_scanned flag to StatusInfo in the data model. Starts
false, set to true after the first Podman scan completes (~15s after
boot). Marketplace now shows a shimmer "Checking..." indicator on app
buttons until the scan finishes, preventing users from accidentally
re-installing apps that are already present but not yet enumerated.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

neode-ui/src/types/api.ts

@@ -37,6 +37,7 @@ export interface StatusInfo {
   'updated': boolean
   'backup-progress': number | null
   'update-progress': number | null
+  'containers-scanned'?: boolean
 }
 
 export type UIMode = 'gamer' | 'easy' | 'chat'