fix(accounting): value foreign-fiat owed openings via the currency asset mark

[TaprootFreak]

Incident

Since the ledger went live on prod, the cutover has been rolling back every 5 minutes in an endless fail-loud retry loop, so the whole ledger stayed inert.

Root cause

openBuyFiatOwed valued a non-CHF owed opening with fiatMark(row.outputAsset.id). But BuyFiat.outputAsset is a Fiat entity — its id is a fiat-table id, not an asset-table id. getMarkAt expects an asset id, so for EUR (fiat id 2) it looked up asset id 2 = a delisted DeFiChain token, found no snapshot mark and threw. The 32 open CHF owed rows passed (hardcoded mark 1); the 6 open EUR rows blocked the entire cutover.

Fix

• fiatMark resolves the fiat currency name to its currency asset(s) via AssetService.getAssetsByName and takes the first candidate carrying a snapshot mark — the same currency-asset route bankMark already uses. A currency with no snapshot mark stays fail-loud (never a silent default).
• Independently hardens the genuinely delisted-crypto case (buy-crypto owed / manual-debt): an opening whose crypto output asset has no mark books asset-backed (native amount + needsMark) so mark-to-market revalues it once a price returns, instead of blocking the whole cutover; the count + assets are warn-logged.
• AssetService is injected as a required dependency (not @Optional() with a runtime throw).

Test plan

• new unit tests: EUR owed valued via the currency-asset mark, CHF via mark 1, no-mark currency stays fail-loud, first-candidate-with-a-mark wins; asset-backed crypto/manual-debt openings + mark-to-market revaluation
• full jest run green, type-check / lint / format:check clean

[TaprootFreak]

Closing as superseded by #4253 (already merged to develop).

This PR and #4253 were parallel fixes for the same incident (the cutover fail-loud rollback loop) with the same root cause (buy_fiat.outputAsset is a Fiat whose id collides with asset ids — fiat 2 = EUR, asset 2 = DeFiChain/dBTC — while the mark cache is asset-keyed). #4253 landed first and resolves it via currencyMark / a markAssetByCurrency map threaded through all foreign-currency paths (buyFiat-owed and bankTx return/repeat/unattributed). This PR's fiatMark-by-name is therefore redundant and would now conflict (its diff is against the pre-#4253 base).

The only delta this PR still had over develop was the asset-backed crypto/manual-debt hardening, which:

• is not exercised by the current cutover (0 feedless open buy_crypto owed rows in the window; both balanceLogDebtPositions assets carry finite snapshot prices), and
• as written, books the owed opening on a per-asset account LIABILITY/{qualifier}/{asset.uniqueName} that no forward discharge path recognises (payout-order/bank-tx consumers match the CHF-bucket name only), so on settlement/return the per-asset liability is never closed and the CHF bucket is over-debited — a latent, silent owed sub-ledger mis-posting.

That hardening, done correctly (per-asset discharge + tests), is tracked in #4270 — non-urgent, defensive/future-proofing for delisted assets.