Implement immutable municipal financial data promotion

## Release gate

PR #114 must not promote local municipal financial data until this is complete.

## Required path

- extend the frozen bundle with detailed line items, census profiles, saved verification checks, and explicit review cutoff
- verify manifest and checksums.sha256 before writes
- bootstrap the source institution release in production after PR #111 deploys
- import into Rails Warehouse tables by natural identity in one transaction, with DRY_RUN=1 and immutable import-audit hash/counts
- upload the bundle, referenced assets, and final coverage/numeric/scale/lineage/issuer/test artifacts to a non-overwritable R2 release prefix
- smoke-test index, Toronto 2025, and an Atlantic record before CanadaSpends deploys

Whole-database copying and production re-extraction are not supported fallbacks. See docs/plans/municipal_financial_statements_deployment.md and docs/reviews/fable_municipal_deployment_review_2026-08-31.md.

Read docs/plans/municipal_financial_statements_deployment.md and docs/reviews/fable_municipal_deployment_review_2026-08-31.md first, then inspect PRs #114 and #111 for release dependencies. Trace the Rails Warehouse import and bundle-release entry points before defining the implementation sequence. Done means the immutable bundle, verified transactional import, non-overwritable R2 prefix, audit artifacts, and all three smoke tests pass after the required production release.

Written by the indexing model from the issue text.