4676a8c5 - Add bank-processing backlog observer (open transactions monitoring)

[TaprootFreak]

Rollout note: deploy this observer first and verify at least two BankProcessing state snapshot: heartbeats in the log pipeline before enabling any downstream consumer of the snapshot lines.

What

Adds a BankProcessingObserver (monitoring subdomain) that watches open bank-processing transactions across five tables — bank_tx, buy_crypto (fiat- and crypto-funded), buy_fiat, fiat_output, bank_tx_return — as 45 declarative invariant rules. Per rule it reports:

• count / chfSum: current backlog and CHF value
• overdueCount / overdueChf: entries older than the rule's tolerance (fixed minutes or a time-of-day/weekend-dependent tolerance in Europe/Zurich)

Every 5 minutes the observer emits the results into the monitoring SystemState and writes structured log lines (a summary heartbeat plus one JSON line per rule). The log lines are a monitoring interface: downstream dashboards parse them, and a missing heartbeat means "monitoring is down" — missing data is never treated as "all clear".

Why

This replaces a legacy spreadsheet-based ops monitor that polled /gs/db and mailed alerts through a retired host (silently broken). The rules were re-derived as invariants on the current schema; per-ID exceptions, manual offsets and stale status values from the legacy rules were deliberately not ported.

Notes for review

• Rules are data (bank-processing.rules.ts); the SQL fragments quote camelCase identifiers for Postgres and were verified against a real Postgres 16 instance.
• Bundled aggregation: one query per base table (CASE sums), not one query per rule. The six statements are separate snapshots; the accepted one-cycle skew is documented in the observer.
• The job registers as a worker-scope cron with its own process gate (BankProcessingMonitoring) and an explicit finite lock timeout (1800s, sibling parity). The monitoring state reaches the API process through the persisted snapshot.
• CHF sums for bank_tx/fiat_output are approximations via fiat.approxPriceChf; non-convertible currencies drop out of the sum (counts stay complete). CHF rounding follows the repo-wide Util.round semantics.
• Non-finite aggregation values fail loud before anything is emitted; a partial run never produces a heartbeat.
• Observe-only: no alerting, no health-check gate in this PR (follow-up once the legacy backlog is triaged).
• The feature is documented for the handbook: docs/bank-processing-monitoring.md (rule model, tolerance semantics, log-line contract, accepted limitations) plus a German metadata entry; the handbook build passes with the new page (21 docs).
• Side change: docs/cron-jobs.md gains the new job row; two pre-existing missing declarations were added and all inventory counts re-derived (142 = 142 self-check).
• Existing aml/payment observers keep their coarser counts; this observer does not touch them.

[TaprootFreak]

4 review passes until zero findings. Fixed along the way: cron-job inventory completeness (including two pre-existing missing declarations), CHF rounding via the shared Util helper, type-level enforcement of the tolerance field, fail-loud guards for non-finite aggregation values, lock-timeout parity with the sibling observers, and adoption of the new mandatory cron scope parameter after rebasing onto the current develop.

[TaprootFreak]

Reworked after the handbook landed on develop: rebased, adopted the mandatory cron scope parameter, and added a handbook-discoverable docs page for the feature (rule model, tolerance semantics, log-line contract) with its metadata entry — the handbook build passes with the new page. Two further review passes on the rework brought the total to 6 passes until zero findings.