feat(storage): mosaic storage migrate-tier with dry-run + idempotency (FED-M1-05)

Adds `mosaic storage migrate-tier --to federated` for one-way migration
from `local` (PGlite) or `standalone` (PG without pgvector) to
`federated` (PG + pgvector). Source is read via DrizzleMigrationSource
which queries the normalized schema (the same path the gateway writes
through), so the migration captures all real domain data — not just
the flat key/value collections.

Key behaviors:
- `--dry-run` prints per-table row counts without writes
- `--allow-non-empty` required to write into a populated target (default
  refuses to mix data sets)
- Per-table transactions; partial failure does not leave half-migrated
  tables
- Idempotent on re-run via INSERT ... ON CONFLICT DO UPDATE keyed on id
- Topological table order respects FK dependencies (verified against
  schema.references())
- Skips sessions, verifications, admin_tokens (TTL'd / one-time / env-bound)
- For sources without pgvector, insights.embedding is projected to NULL
  on read, then upserted as NULL (column is nullable)

32 unit tests cover ordering, dry-run, idempotency, empty-target
preconditions, table skipping, and embedding-null projection. Integration
test against real PG/PGlite is FED-M1-08.

Refs #460

packages/storage/src/index.ts

@@ -3,6 +3,25 @@ export { createStorageAdapter, registerStorageAdapter } from './factory.js';
 export { PostgresAdapter } from './adapters/postgres.js';
 export { PgliteAdapter } from './adapters/pglite.js';
 export { registerStorageCommand } from './cli.js';
+export {
+  getMigrationOrder,
+  topoSort,
+  runMigrateTier,
+  checkTargetPreconditions,
+  normaliseSourceRow,
+  PostgresMigrationTarget,
+  DrizzleMigrationSource,
+  SKIP_TABLES,
+  MIGRATION_ORDER,
+  MigrationPreconditionError,
+} from './migrate-tier.js';
+export type {
+  MigrationSource,
+  MigrationTarget,
+  MigrateTierOptions,
+  MigrateTierResult,
+  TableMigrationResult,
+} from './migrate-tier.js';
 
 import { registerStorageAdapter } from './factory.js';
 import { PostgresAdapter } from './adapters/postgres.js';