Virtualization: a disk-location picker on both create forms, locations by place, add or remove a location

Pools are shown by where their bytes land (plain files on this disk, a ZFS pool inside one
file, a dataset…) rather than by driver name, which read as the NAS pool. A location can be
added as a plain-files pool at any folder on the machine, and removed while nothing uses it.
The driver order at Install is as it was; the labels say what each one really is.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/storage/snapshots.go

@@ -66,7 +66,6 @@ type Policy struct {
 	KeepMin int    `json:"keep_min"`
 	Prefix  string `json:"prefix"`
 	Enabled bool   `json:"enabled"`
-
 }
 
 func (p *Policy) prefix() string { return strings.TrimSpace(p.Prefix) }