test(storage): integration test for migrate-tier PGlite → federated PG (FED-M1-08)

Seeds a temp PGlite with representative cross-table data (users, teams,
team_members, conversations, messages), runs mosaic storage migrate-tier
against a live federated PG+pgvector profile, asserts exact row counts and
spot-checks key columns. Gated by FEDERATED_INTEGRATION=1.

Caught and fixed P0 bug in migrate-tier:

  PostgresMigrationTarget passed Drizzle-selected camelCase keys
  (emailVerified, userId, ...) verbatim as SQL identifiers, failing on
  Postgres which expects snake_case. The 32 unit tests missed this because
  both source and target were mocked. normaliseSourceRow now applies
  toSnakeCase conversion that is idempotent on already-snake_case keys.

Test infrastructure:

- packages/storage/src/test-utils/pglite-with-vector.ts: PGlite +
  @electric-sql/pglite/vector (JS-native pgvector) and migration runner.
  Co-located with storage tests rather than exposed on @mosaicstack/db
  public surface (would have polluted prod consumers with WASM bundle).
- packages/storage now declared "type": "module" (codebase convention,
  required for import.meta.url in test-utils).

afterAll cleanup deletes prefix-namespaced rows even on test panic.

Refs #460

packages/storage/package.json

@@ -6,6 +6,7 @@
     "url": "https://git.mosaicstack.dev/mosaicstack/stack.git",
     "directory": "packages/storage"
   },
+  "type": "module",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
   "exports": {
@@ -29,6 +30,7 @@
     "postgres": "^3.4.8"
   },
   "devDependencies": {
+    "drizzle-orm": "^0.45.1",
     "typescript": "^5.8.0",
     "vitest": "^2.0.0"
   },