feat(storage): add registerStorageCommand for mosaic storage CLI surface

Implements CU-05-02: adds `mosaic storage` command group with subcommands
status, tier show, tier switch, export, import, and migrate. Pragmatic
stubs print actionable instructions for unimplemented export/import tiers.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/mosaic/package.json

@@ -34,6 +34,7 @@
     "@mosaicstack/prdy": "workspace:*",
     "@mosaicstack/quality-rails": "workspace:*",
     "@mosaicstack/queue": "workspace:*",
+    "@mosaicstack/storage": "workspace:*",
     "@mosaicstack/types": "workspace:*",
     "@clack/prompts": "^0.9.1",
     "commander": "^13.0.0",