tower 0.61.1 — Phase F (B): tenant-scoped S3 resolver

Refactor s3Resolver from a single-global-creds reader into a
tenant-scoped factory. Each tenant brings their own S3 endpoint,
region, three named buckets (backups + templates + audit), and
access keys (in Vault at v3/tenants/<id>/s3-credentials).

Touches:
  s3.go         — s3Resolver becomes factory; tenantS3 wraps
                  one minio.Client + bucket per tenant
  audit.go      — events grouped by tenantID per flush, written
                  to the tenant's audit bucket
  backups.go    — fleet view fans out one S3 LIST per tenant;
                  per-instance handlers resolve via Argo App
  export/import/migrate — tenant resolved from Argo App label
                  or scope.TenantID
  templates_*   — per-template tenant lookup via templateTenantID
                  (platform tenant for OwnerPlatform manifests)
  vitals.go     — last-backup probe pulls tenantID before list

Adds AllTenants() to PlatformStore so the templates orphan sweep
can iterate every tenant configured with a templates bucket.

Build: tower:0.61.1 — pushed to registry.odoosky.cloud

values.yaml

@@ -9,7 +9,7 @@ backend:
     # so every cluster that runs Tower needs the same imagePullSecret
     # provisioned out-of-band (until cluster-platform-v3 owns it).
     repository: registry.odoosky.cloud/odoosky/docker-mirror/tower
-    tag: "0.61.0"
+    tag: "0.61.1"
     pullPolicy: IfNotPresent
   imagePullSecrets:
     - name: docker-mirror-pull