Add national municipal financial statement API

[xrendan]

Summary

• add reviewed detailed municipal financial statement extraction, validation, and saved checks
• expose national municipal index/detail APIs with historical years, Sankey line items, census context, and normalized Ontario/Alberta names
• add resumable processing, jurisdiction-specific recovery, audit/finalization scripts, and deployment runbook

Stack

Stacked on #111. Merge that parent first. The data release remains gated on national finalization and verified production promotion.

Verification

• 160 focused Rails tests, 650 assertions, 0 failures
• RuboCop: 141 files, no offenses
• local API/UI smoke: 2,084 municipalities, 12,890 statements, all 13 jurisdictions
• Toronto 2025: 94 saved checks and Sankey
• Grand-Bouctouche 2023: 90 saved checks and Sankey

Deployment

See docs/plans/municipal_financial_statements_deployment.md. Deploy York schema/API before promoting data or deploying CanadaSpends. This PR is draft while extraction finalization and the reviewed local-to-production data handoff are pending.

[xrendan]

Companion frontend PR: BuildCanada/CanadaSpends#277

Claude Fable deployment review is recorded in docs/reviews/fable_municipal_deployment_review_2026-08-31.md. The reviewed path now requires a source-release bootstrap, production preflight, immutable R2 evidence, and a verified Warehouse importer before data promotion.

[xrendan]

Production data-promotion gate is tracked in #115. York CI is now green on commit 3bdb338.