feat(invoices): quarterly, half-yearly and yearly recurring invoice schedules (#1438)

* fix(mcp): offer the link tool in the uncategorized-transactions VAT blocker

The gnubok_vat_close_check blocker hint only named categorize/auto-match,
both of which create new bookkeeping. For a transaction whose
affarshandelse is already booked on an existing verifikat, following the
hint would double-book, so agents dead-ended the case into "contact
support" (2026-08-06 support mail from Orto Engineering). The hint now
also names gnubok_link_transaction_to_journal_entry, is extracted as an
exported constant pinned by a test, and the tool joins the
categorize_month recommended loadout.

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

* feat(invoices): quarterly, half-yearly and yearly recurring schedules

User request: recurring invoice schedules only supported monthly cadence.
Adds interval_months (SMALLINT 1-12, default 1) to
recurring_invoice_schedules; the UI offers manadsvis/kvartalsvis/
halvarsvis/arsvis presets while API and MCP accept any 1-12.

The cron advances next_run_date by whole intervals from the due date, and
the new rollNextRunDateForward() helper rolls missed or edited interval
schedules on their own month grid so a quarterly Jan/Apr/Jul/Oct schedule
missed in an outage rolls Jan 15 to Apr 15, never Feb 15. Monthly
(interval 1) keeps its existing today-anchored recompute semantics
unchanged. Changing the interval alone never touches next_run_date: the
new cadence applies from the next run, so an edit can never pull a send
earlier.

Existing rows default to 1 and behave byte-identically. The MCP slice of
this feature (interval_months on the three recurring-schedule tools in
server.ts) was committed in d2600907f alongside the VAT-blocker hint fix
by a parallel session sharing this worktree.

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

* fix(invoices): address PR #1438 review findings

CodeRabbit round 1, all three findings:
- MCP descriptions now state the full accepted interval range (any integer
  1-12) instead of enumerating only the 1/3/6/12 presets, and qualify that
  changing ONLY interval_months leaves next_run_date untouched.
- assertValidCadence rejects fractional day_of_month.
- rollNextRunDateForward rejects calendar-invalid anchors that pass the
  shape regex (2026-13-05, 2026-02-31), with regression tests.

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

---------

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

components/invoices/NewRecurringScheduleDialog.tsx

@@ -112,6 +112,7 @@ function NewRecurringScheduleForm({
       customer_id: z.string().uuid(t('validation_customer_required')),
       name: z.string().min(1, t('validation_name_required')),
       day_of_month: z.number().int().min(1).max(31),
+      interval_months: z.number().int().min(1).max(12),
       send_hour: z.number().int().min(0).max(23),
       payment_terms_days: z.number().int().min(0).max(90),
       currency: z.enum(['SEK', 'EUR', 'USD', 'GBP', 'NOK', 'DKK']),
@@ -139,6 +140,7 @@ function NewRecurringScheduleForm({
           customer_id: schedule.customer_id,
           name: schedule.name,
           day_of_month: schedule.day_of_month,
+          interval_months: schedule.interval_months ?? 1,
           send_hour: schedule.send_hour ?? 8,
           payment_terms_days: schedule.payment_terms_days,
           currency: schedule.currency,
@@ -163,6 +165,7 @@ function NewRecurringScheduleForm({
           customer_id: '',
           name: '',
           day_of_month: 15,
+          interval_months: 1,
           send_hour: 8,
           payment_terms_days: 30,
           currency: 'SEK',
@@ -296,6 +299,37 @@ function NewRecurringScheduleForm({
           </div>
 
           <div className="grid grid-cols-1 sm:grid-cols-2 gap-4">
+            <div>
+              <Label htmlFor="interval_months">{t('interval_label')}</Label>
+              <Controller
+                control={control}
+                name="interval_months"
+                render={({ field }) => (
+                  <Select
+                    value={String(field.value)}
+                    onValueChange={(v) => field.onChange(Number(v))}
+                  >
+                    <SelectTrigger id="interval_months">
+                      <SelectValue />
+                    </SelectTrigger>
+                    <SelectContent>
+                      <SelectItem value="1">{t('interval_monthly')}</SelectItem>
+                      <SelectItem value="3">{t('interval_quarterly')}</SelectItem>
+                      <SelectItem value="6">{t('interval_semiannual')}</SelectItem>
+                      <SelectItem value="12">{t('interval_yearly')}</SelectItem>
+                      {/* A non-preset interval (set via API/MCP, e.g. every 2
+                          months) must stay selectable so an edit doesn't
+                          silently coerce it to a preset. */}
+                      {![1, 3, 6, 12].includes(field.value) && (
+                        <SelectItem value={String(field.value)}>
+                          {t('interval_every_n', { n: field.value })}
+                        </SelectItem>
+                      )}
+                    </SelectContent>
+                  </Select>
+                )}
+              />
+            </div>
             <div>
               <Label htmlFor="day_of_month">{t('day_label')}</Label>
               <Input