feat(WHE-29): add v1 accounting schema migration and seed fixtures

docs/runbooks/dev-setup.md

@@ -25,6 +25,7 @@ bun run build
 bun run db:generate
 bun run db:check
 bun run db:migrate
+bun run db:seed
 bun run infra:fmt:check
 bun run infra:validate
 ```

docs/runbooks/migrations.md

@@ -58,3 +58,12 @@ bun run build
   2. Data backfill/cutover
   3. Cleanup migration
 - Never run `db:push` in production pipelines.
+
+## Rollback notes
+
+- If a migration fails mid-run, stop deploy and inspect `drizzle.__drizzle_migrations` state first.
+- For additive migrations in v1, rollback by:
+  1. Reverting application code to previous release.
+  2. Leaving additive schema in place (safe default).
+- For destructive migrations, require explicit rollback SQL script in the same PR before deploy approval.
+- Keep one database backup/snapshot before production migration windows.