Supp/verifikationer inconsitency (#369)

* feat(bookkeeping): implement reset bookkeeping functionality with safeguards

* feat(migrations): restore relaxed trigger for retroactive first fiscal year

supabase/migrations/20260427160000_restore_retroactive_first_fiscal_year.sql

@@ -0,0 +1,38 @@
+-- Restore retroactive first fiscal year fix.
+--
+-- Migration 20260418120000 (applied to prod as 20260420092940
+-- "allow_retroactive_first_fiscal_year") relaxed the trigger so that a
+-- mid-month period_start is allowed when no existing period starts earlier.
+--
+-- However, on prod the migration "sie_files_and_fiscal_period_sync" was
+-- recorded with version 20260421194554 — *after* the fix — and its body
+-- contains a CREATE OR REPLACE FUNCTION with the strict pre-fix logic,
+-- which clobbered the relaxed trigger. As a result the SIE import flow
+-- for förlängt första räkenskapsår started failing again on prod.
+--
+-- This migration re-applies the relaxed trigger so that mid-month start
+-- is allowed iff no existing period starts earlier.
+
+CREATE OR REPLACE FUNCTION public.enforce_first_of_month_for_subsequent_periods()
+RETURNS trigger
+LANGUAGE plpgsql
+AS $$
+BEGIN
+  IF EXTRACT(DAY FROM NEW.period_start) = 1 THEN
+    RETURN NEW;
+  END IF;
+
+  IF EXISTS (
+    SELECT 1 FROM public.fiscal_periods
+    WHERE company_id = NEW.company_id
+      AND id IS DISTINCT FROM NEW.id
+      AND period_start < NEW.period_start
+  ) THEN
+    RAISE EXCEPTION 'Non-first fiscal period must start on the 1st of a month';
+  END IF;
+
+  RETURN NEW;
+END;
+$$;
+
+NOTIFY pgrst, 'reload schema';