chore: update go-cs3apis to latest (Jun 2026)

[flash7777]

Summary

Update go-cs3apis to v0.0.0-20260604164754-c3fdb0aa5e9e (Jun 4 2026).

Three upstream cs3apis changes require adaptations:

1. feat: add container-specific permissions and immutable flag cs3org/cs3apis#272 — adds SetImmutable/UnsetImmutable RPCs to ProviderAPI
2. ocm: add TRANSFERRING share state cs3org/cs3apis#273 — OCM share state changes
3. Labels API — AddLabel/RemoveLabel moved from StorageProvider to cs3/labels/v1beta1

Labels API Migration

Before (old cs3apis):

  opencloud ──AddLabel──► Gateway ──c.AddLabel()──► StorageProvider
  (graph)    provider.Req          ProviderAPIClient (ProviderAPI)
                                                     → Storage.AddLabel()

After (this PR):

  opencloud ──AddLabel──► Gateway ──lc.AddLabel()──► StorageProvider
  (graph)    labels.Req            LabelsAPIClient   (LabelsAPI service)
                                                     → Storage.AddLabel()

The StorageProvider now registers as LabelsAPIServer in addition to
ProviderAPIServer and SpacesAPIServer. The Gateway routes Labels calls
via a new LabelsAPIClient using the same GRPC connection pool.

AddLabel/RemoveLabel continue to work end-to-end. The only change
is the GRPC service name — the underlying Storage FS implementation is
unchanged.

Changes

• go.mod: bump go-cs3apis
• StorageProvider: register as LabelsAPIServer, implement AddLabel/RemoveLabel/ListLabels/ListResourcesForLabel via Storage FS interface
• Gateway: route AddLabel/RemoveLabel to StorageProvider's LabelsAPI service
• Pool: add LabelsProviderSelector and GetLabelsProviderServiceClient
• All ProviderAPI implementations: add SetImmutable/UnsetImmutable stubs
• Regenerate mocks

Test plan

• Full build passes (go build ./...)
• Labels (favorites) still work end-to-end
• CI pipeline