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_volume_tier_compact.go

@@ -126,6 +126,39 @@ func (c *commandVolumeTierCompact) Do(args []string, commandEnv *CommandEnv, wri
 	return nil
 }
 
+// findVolumeCollection resolves the collection a volume actually lives in,
+// honoring the -collection filter: an empty pattern matches any collection, a
+// non-empty one compiles like the rest of the tier commands. The volume server
+// verifies the collection name on tier requests, so callers need the real
+// name, not the pattern.
+func findVolumeCollection(topoInfo *master_pb.TopologyInfo, vid needle.VolumeId, collectionPattern string) (collection string, found bool, err error) {
+	var matchesCollection func(string) bool
+	if collectionPattern != "" {
+		collectionMatcher, compileErr := compileCollectionPattern(collectionPattern)
+		if compileErr != nil {
+			return "", false, fmt.Errorf("invalid collection pattern '%s': %v", collectionPattern, compileErr)
+		}
+		matchesCollection = collectionMatcher.Matches
+	} else {
+		matchesCollection = func(string) bool { return true }
+	}
+
+	eachDataNode(topoInfo, func(dc DataCenterId, rack RackId, dn *master_pb.DataNodeInfo) {
+		if found {
+			return
+		}
+		for _, diskInfo := range dn.DiskInfos {
+			for _, v := range diskInfo.VolumeInfos {
+				if needle.VolumeId(v.Id) == vid && matchesCollection(v.Collection) {
+					collection, found = v.Collection, true
+					return
+				}
+			}
+		}
+	})
+	return
+}
+
 func findRemoteVolumeInTopology(topoInfo *master_pb.TopologyInfo, vid needle.VolumeId, collectionPattern string) (remoteVolumeInfo, bool, error) {
 	var matchesCollection func(string) bool
 	if collectionPattern != "" {