fix(app): 503 on storage failures, validated currency, lock release on shutdown, per-IP login limit, unit-only npm test

test(ledger): same-instance compaction retries, heal-path put faults, real in-flight write test

fix(ledger): writer guard re-checks ownership and self-demotes on stale heartbeat

test(ledger): prove compaction crash safety with fault injection and against the real bucket

feat(ledger): add heartbeat-based writer guard

fix(ledger): heal truncated ledger, validate events on write, reconcile pending

feat(ledger): add Ledger service with event write path and compaction

feat(ledger): add event schema, jsonl encoding and fold