Add operator storage support to TDN format

Export/import operator .storage dictionaries in TDN files. Primitive
types serialize directly; tuple, set, and bytes use $type/$value
wrappers. Transient Embody keys (envoy_running, _git_root, etc.) are
excluded. Phase 6a restores storage after DAT content, before positions.
startup_storage entries use storeStartupValue() for project-open reset.

Includes 43 new tests across helpers, export/import, and reconstruction
suites. Updated TDN specification and JSON schema.

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