fix(nfs): reconcile clients[i].advanced type mismatch (object vs string)

backend: db.NFSClient.Advanced is db.NFSAdvanced (struct → JSON object)
handler: nfsClientRequest.Advanced was string → now db.NFSAdvanced
frontend: api.ts NFSClient.advanced string → NFSAdvanced (object)
frontend: Nfs.tsx updated to work with object advanced per host

Without this fix, editing an existing NFS export with per-host options
(loaded from DB via migration 0005) would 400 on PUT because the
backend expected a string but received a JSON object.

internal/web/handlers_nfs.go

@@ -14,12 +14,12 @@ import (
 )
 
 type nfsClientRequest struct {
-	Host         string `json:"host"`
-	ReadOnly     bool   `json:"read_only"`
-	Async        bool   `json:"async"`
-	RootSquash   bool   `json:"root_squash"`
-	SubtreeCheck bool   `json:"subtree_check"`
-	Advanced     string `json:"advanced"`
+	Host         string          `json:"host"`
+	ReadOnly     bool            `json:"read_only"`
+	Async        bool            `json:"async"`
+	RootSquash   bool            `json:"root_squash"`
+	SubtreeCheck bool            `json:"subtree_check"`
+	Advanced     db.NFSAdvanced  `json:"advanced"`
 }
 
 type nfsExportRequest struct {
@@ -54,7 +54,7 @@ func (req nfsExportRequest) toModel() db.NFSExport {
 			Async:        c.Async,
 			RootSquash:   c.RootSquash,
 			SubtreeCheck: c.SubtreeCheck,
-			Advanced:     parseNFSAdvanced(c.Advanced),
+			Advanced:     c.Advanced,
 		})
 	}
 	return db.NFSExport{
@@ -68,15 +68,6 @@ func (req nfsExportRequest) toModel() db.NFSExport {
 	}
 }
 
-func parseNFSAdvanced(raw string) db.NFSAdvanced {
-	var adv db.NFSAdvanced
-	if raw == "" || raw == "{}" {
-		return adv
-	}
-	_ = json.Unmarshal([]byte(raw), &adv)
-	return adv
-}
-
 func (s *Server) handleListNFSExports(w http.ResponseWriter, r *http.Request) {
 	exports, err := s.DB.ListNFSExports()
 	if err != nil {