shell: make every -collection flag parse the same way (#11794)

* shell: make every -collection flag parse the same way

The filter vocabulary (comma-separated names, wildcards, regexes,
"_default" for the empty-named collection) already existed in
wildcard.CompileCollectionMatcher, but several commands still did their
own exact-match comparison or sent the raw flag value to servers.

fs.mergeVolumes used a literal string compare, so -collection=_default
silently produced an empty merge plan; it now uses the shared matcher
while keeping "*" as the match-all default. volume.fsck and volume.mark
filter through the matcher too, and volume.vacuum resolves the filter
client-side into per-collection and per-volume requests, since no
Collection value scopes the VacuumVolume RPC to the unnamed collection
alone.

Commands that put one concrete collection name on the wire normalize
"_default" to "" (volume.grow, fs.configure, mq.topic.compact,
collection.delete, ec.rebuild, ec.balance), and the tier -volumeId
commands resolve the volume's actual collection from topology first so
patterns and named-collection requests pass the volume server's
collection check.

* shell: spell the default-collection keyword via CollectionDefault

* shell: address review findings on collection filter handling

volume.fsck keeps a set of every volume the master knows before any
filtering, so a filer entry whose volume was excluded by -collection or
-volumeId is skipped instead of reported "volume not found" and deleted
by -reallyDeleteFilerEntries. The collection filter also no longer
scopes the filer walk to /buckets/<collection>: fs.configure can bind a
collection to any path prefix, and a narrower walk could mark live
chunks as orphans under -reallyDeleteFromVolume.

ec.rebuild and ec.balance resolve -collection through the new
wildcard.ExpandCollectionFilter, which passes literal names through even
when the master does not list them — ec.rebuild must be able to recover
a collection whose shards all lost their index and never registered.

fs.configure and mq.topic.compact now reject _default outright: an empty
Collection means "unset" in both the path-rule merge and the filer's
storage-option fallback chain, so the keyword would have been silently
ignored.

The unnamed-collection vacuum sweep keeps the master's low-disk-space
exception: a volume whose every replica is read-only is probed with
VacuumVolumeCheck and stays eligible when a replica reports
DiskSpaceLow, instead of being dropped outright.

weed/shell/command_collection_delete.go

@@ -35,7 +35,7 @@ func (c *commandCollectionDelete) HasTag(CommandTag) bool {
 func (c *commandCollectionDelete) Do(args []string, commandEnv *CommandEnv, writer io.Writer) (err error) {
 
 	colDeleteCommand := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
-	collectionName := colDeleteCommand.String("collection", "", "collection to delete. Use '_default_' for the empty-named collection.")
+	collectionName := colDeleteCommand.String("collection", "", "collection to delete. Use '"+CollectionDefault+"' for the empty-named collection.")
 	applyBalancing := colDeleteCommand.Bool("apply", false, "apply the collection")
 	// TODO: remove this alias
 	applyBalancingAlias := colDeleteCommand.Bool("force", false, "apply the collection (alias for -apply)")
@@ -55,9 +55,13 @@ func (c *commandCollectionDelete) Do(args []string, commandEnv *CommandEnv, writ
 		return fmt.Errorf("empty collection name is not allowed")
 	}
 
-	if *collectionName == "_default_" {
+	// The legacy "_default_" spelling stays accepted for compatibility;
+	// CollectionDefault is the shared keyword every other -collection flag
+	// uses for the empty-named collection.
+	if *collectionName == CollectionDefault+"_" {
 		*collectionName = ""
 	}
+	*collectionName = resolveCollectionName(*collectionName)
 
 	if !*applyBalancing {
 		fmt.Fprintf(writer, "collection '%s' will be deleted. Use -apply to apply the change.\n", *collectionName)