diskUsage now carries Sources []string instead of a single Source.
collectDiskUsage accumulates all sources (samba, nfs, manual) per path.
NFS no longer adds a redundant label to used_by.
Dashboard and Settings render one chip per source. When a path
is shared via SMB and NFS, both chips appear.
API breaking: disks[].source replaced by disks[].sources[].
Version: 0.2.1 -> 0.3.0