feat(deadlines): gate F-skatt reminders on debited preliminary tax + durable dismissal (#1057)

* feat(deadlines): gate F-skatt reminders on debited preliminary tax, add durable dismissal

The f_skatt deadline was gated on the F-skatt approval flag (DB default
true), giving nearly every company 12 monthly payment reminders for a tax
Skatteverket may not have debited at all (64% of all system deadline rows,
one lifetime completion). Approval carries no recurring obligation; the
monthly duty is payment of debiterad preliminarskatt and exists only while
the debited amount is > 0 (SFL 62 kap. 4-5 par., 55 kap. 2 par.).

- Gate the f_skatt deadline on preliminary_tax_monthly > 0 (field already
  collected at onboarding, previously unread) and retitle it as a payment.
- Storforetag keep the 12th in August (January-only 17th, 62 kap. 3 par.).
- Declare the prod-only preliminary_tax_monthly column in a migration so
  installs built purely from migrations stop failing tax-settings saves.
- Add deadlines.dismissed_at: DELETE on a system deadline now soft-dismisses
  it durably (hard deletes were resurrected by the nightly backfill within
  24h); generator, backfill, and every read surface respect it.
- Prune upcoming f_skatt rows for companies with no debited amount.

Closes part of #1028.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(deadlines): include dismissed_at in DeadlineForm payload

The Deadline type gained the required dismissed_at field; the form's
submit payload literal must carry it for the Omit<Deadline, ...> shape.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(deadlines): make system-deadline dismissal atomic

Constrain the dismiss update to source='system' and verify a row was
actually updated: a concurrent regeneration can delete the row between
lookup and update, and the route must not report a phantom success.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

types/index.ts

@@ -2215,6 +2215,9 @@ export interface Deadline {
   reminder_offsets: number[] | null
   status: DeadlineStatus
   status_changed_at: string
+  // Durable opt-out for system deadlines: hidden everywhere, never
+  // recreated by the generator or the backfill cron.
+  dismissed_at: string | null
   linked_report_type: string | null
   linked_report_period: Record<string, unknown> | null
 
@@ -2340,7 +2343,7 @@ export const TAX_DEADLINE_TYPE_LABELS: Record<TaxDeadlineType, string> = {
   moms_monthly: 'Momsdeklaration (månad)',
   moms_quarterly: 'Momsdeklaration (kvartal)',
   moms_yearly: 'Momsdeklaration (år)',
-  f_skatt: 'F-skatt',
+  f_skatt: 'Preliminärskatt (F-skatt)',
   arbetsgivardeklaration: 'Arbetsgivardeklaration',
   skatteinbetalning: 'Skatteinbetalning (storföretag)',
   inkomstdeklaration_ef: 'Inkomstdeklaration EF',