admin: default -dataDir to "." so maintenance task state persists across restarts (#9856)

admin: default -dataDir to "." so maintenance task state persists

Previously -dataDir defaulted to empty, so the admin ran maintenance in
memory only: task state was never saved and maintenance tasks (notably EC
balance/rebuild) were re-issued every scan cycle without converging,
churning EC shards (moves landed shards without their .ecx index, leaving
EC volumes unloadable/missing shards).

Default -dataDir to "." (the process working directory, which under the
standard systemd unit is the admin's data dir) so state persists out of
the box.

weed/command/admin.go

@@ -65,7 +65,7 @@ func init() {
 	a.grpcPort = cmdAdmin.Flag.Int("port.grpc", 0, "gRPC server port for worker connections (default: http port + 10000)")
 	a.master = cmdAdmin.Flag.String("master", "localhost:9333", "comma-separated master servers")
 	a.masters = cmdAdmin.Flag.String("masters", "", "comma-separated master servers (deprecated, use -master instead)")
-	a.dataDir = cmdAdmin.Flag.String("dataDir", "", "directory to store admin configuration and data files")
+	a.dataDir = cmdAdmin.Flag.String("dataDir", ".", "directory to store admin configuration and data files (default current dir; required for maintenance task state to persist)")
 
 	a.adminUser = cmdAdmin.Flag.String("adminUser", "admin", "admin interface username")
 	a.adminPassword = cmdAdmin.Flag.String("adminPassword", "", "admin interface password (if empty, auth is disabled)")
@@ -248,7 +248,6 @@ func runAdmin(cmd *Command, args []string) bool {
 		fmt.Println("WARNING: Admin interface is running without authentication!")
 		fmt.Println("         Set -adminPassword for production use")
 	}
-
 	fmt.Printf("Starting SeaweedFS Admin Interface on port %d\n", *a.port)
 	fmt.Printf("Worker gRPC server will run on port %d\n", *a.grpcPort)
 	fmt.Printf("Masters: %s\n", *a.master)