GET  /api/vault/status     index health
POST /api/vault/upload     multipart upload (BoB CSV/PDF/XLSX)
POST /api/vault/scan       reindex
POST /api/vault/query      natural-language Q&A
POST /api/vault/search     keyword search
GET  /api/vault/list       browse files
POST /api/vault/read       read file
POST /api/vault/summary    summarize file