fix(bookkeeping): book pre-FY bank transactions on the fiscal year's first day (#1828)

A newly registered company whose first rakenskapsar starts on the
Bolagsverket registration date could not book the aktiekapital deposit,
because the bank transaction is dated BEFORE the registration. Every
surface dead-ended: the manual booking dialog hard-blocked with the date
locked and only offered creating a (legally wrong) pre-registration
fiscal year, and the categorize paths either marked the row categorized
WITHOUT a verifikat ("Delvis bokforda") or silently minted a bogus
calendar-year period before the company existed.

Root cause: entry_date was hard-wired to the bank date with no clamp
against the company's first fiscal period, and the duplicated
ensureFiscalPeriod helpers upserted a calendar-year period for any
uncovered date.

Fix, per BFL (the event belongs to the first fiscal year; the real
affarshaendelse date is preserved on the verifikat):
- createTransactionJournalEntry clamps a pre-FY date into the earliest
  OPEN unlocked fiscal period with entry_date = period_start and appends
  "Affarshaendelse <date>, bokford pa rakenskapsarets forsta dag" to the
  verifikationstext. Interior gaps, future dates, and a closed/locked
  first year keep the old null return.
- Both ensureFiscalPeriod copies (categorize core + web route) skip the
  calendar-period upsert when the date predates the earliest period.
- JournalEntryForm's no_period block offers "Bokfor pa rakenskapsarets
  forsta dag (<date>)" for pre-FY dates instead of proposing a
  pre-registration year; "Skapa rakenskapsar" remains for the other
  no_period cases.

No schema, RPC, or trigger changes: the /book route and the DB triggers
already accept the clamped booking.

Fixes #1825


Claude-Session: https://claude.ai/code/session_01SyDuePXxUFowaPBKpAv8SF

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

lib/pending-operations/__tests__/commit-duplicate-guard.test.ts

@@ -121,8 +121,10 @@ describe('commit duplicate guard: categorize_transaction (reverse / book the ban
       { data: { id: 'tx-1', date: '2026-03-26', amount: 98565, cash_account_id: null, journal_entry_id: null } },
       { data: { entity_type: 'aktiebolag', fiscal_year_start_month: 1 } },
       { data: [] }, // no fiscal period yet
+      { data: [] }, // pre-FY guard: earliest-period lookup (none yet)
       { data: null }, // fiscal-period upsert
       { data: null }, // journal-entry period lookup: partial categorization path
+      { data: [] }, // pre-FY clamp: earliest-period lookup (none yet)
       {
         data: [{
           id: 'tx-1',
@@ -169,8 +171,10 @@ describe('commit duplicate guard: categorize_transaction (reverse / book the ban
       { data: { id: 'tx-1', date: '2026-03-26', amount: 98565, cash_account_id: null, journal_entry_id: null } },
       { data: { entity_type: 'aktiebolag', fiscal_year_start_month: 1 } },
       { data: [] }, // no fiscal period yet
+      { data: [] }, // pre-FY guard: earliest-period lookup (none yet)
       { data: null }, // fiscal-period upsert
       { data: null }, // journal-entry period lookup: partial categorization path
+      { data: [] }, // pre-FY clamp: earliest-period lookup (none yet)
       {
         data: [{
           id: 'tx-1',