fix(skattekonto): remove the drift email, its event and the unused drift route (#2149)

The nightly skattekonto sync emailed "Skattekontot stämmer inte med
bokföringen" whenever Skatteverket's saldo differed from BAS 1630 by more
than 1 kr, every 24 hours while it lasted. On 2026-09-02 it fired on a
35 842 kr gap that the reconciliation explained to the last krona with 14
unbooked rows, while the Hem notice and the reconciliation page (both
gated on unexplained_difference) said nothing was wrong.

The check shipped in May 2026 (#525) before any in-app skattekonto view
existed; the dashboard tile its comments promise was never built and the
drift API route had no consumer. Since 2026-08-25 the reconciliation page
and the Hem notice are the surface, with one definition of "stämmer inte".

Removed: skattekonto-drift.ts, skattekonto-drift-email.ts, their tests,
the skattekonto.drift_detected event type, the handler registration, the
cron's drift hook, GET /api/extensions/skatteverket/skattekonto/drift, and
the ROPA activity for the mail. The route is dropped from the ungated
extension route allowlist to lock the ratchet. skattekonto_drift_tolerance
stays: the Hem notice reads it. Stale skattekonto_drift_last_alert_at rows
in extension_data are inert.

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

DECISIONS.md

@@ -1482,3 +1482,4 @@ One line per decision: `[YYYY-MM-DD] <decision>: <why>`. Appended by agents and
 
 [2026-09-01] ENABLE_BANKING_SANDBOX removed from the enable-banking manifest and the index.ts header (#2131): the variable was declared as optional but never read anywhere; sandbox vs production is decided by ENABLE_BANKING_API_URL (api.tilisy.com vs api.enablebanking.com, api-client.ts derives isSandbox from the host). A dead variable declared in the manifest is what the self-hosting docs would otherwise have copied. The manifest now lists the two optional variables the code actually reads (API_URL, PSU_TYPE); the _PRODUCTION aliases stay undeclared on purpose, they are a hosted Vercel convention, not an operator contract.
 [2026-09-01] PR #2130 security-scan round: the register's djuplank is validated (https + skatteverket.se host) before it is returned or navigated to, since the settings page follows it; a contested org number now WITHDRAWS an already-recorded grant nightly (not only blocks new ones), outside the downgrade guards on purpose. NOT done: proof of org-number ownership (Bolagsverket firmatecknare / BankID) before any ombud grant; the org number is tenant-editable across the product (AGI, invoices, årsredovisning) and binding it to a verified identity is a product decision for Emil, tracked as a follow-up rather than declined.
+[2026-09-02] Removed the skattekonto drift email (skattekonto.drift_detected event, handler, /api/extensions/skatteverket/skattekonto/drift route, cron hook) instead of fixing it: it alerted on raw saldo-vs-1630 gaps that unbooked rows explain by construction (2026-09-02: Arcim 35 842 kr, 100% explained, while the Hem notice and reconciliation page said nothing was wrong), repeated every 24 h, and was the only surface of a May-2026 feature whose promised dashboard tile was never built. Since 2026-08-25 the reconciliation page and the Hem notice (detectSkvUnexplained, gated on unexplained_difference) are the surface. Considered gating the mail on unexplained_difference + once per episode (built, then dropped): after that gate it only fires on integrity findings the engine itself calls 'never a user task'. skattekonto_drift_tolerance stays (Hem notice reads it); stale skattekonto_drift_last_alert_at rows in extension_data are inert.