feat(calendar): enable calendar sync for Viktiga datum (#1853)

Turns on the calendar extension (built Feb 2026, stripped in the 2026-03-02 production readiness deploy, never re-enabled): ICS feed settings, calendar workspace, subscribe button on the Viktiga datum page.

Hardening before first real use: feed serve route now requires the creator to still be a company member (offboarding stops the feed); stable pagination (due_date + id, dedupe) on feed queries; fetches inside the logged try block; invoice events limited to sent/paid/partially_paid/overdue; event UIDs rebranded to accounted.se while zero feeds exist; APP_URL fallback fails closed in production; mobile stacking for the deadlines header; settings note that Google Calendar needs default notifications on subscribed calendars; calendar workspace aligned with the design system.

Skeptic reviewed (3 refutations, all fixed) plus one compliance swarm finding (fixed). No migrations.

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

components/settings/CalendarFeedSettings.tsx

@@ -230,6 +230,10 @@ export function CalendarFeedSettings() {
           </SettingsRowEnd>
         </SettingsRow>
 
+        <p className="px-1 pt-2 text-xs text-muted-foreground">
+          {t('google_reminders_note')}
+        </p>
+
         <SettingsRow label={t('create_new_link')} help={t('regen_help')}>
           {/* Live feed stats stay visible: they are state, not instructions */}
           {feed.last_accessed_at && (