fix: close all remaining known gaps across modules

Every 'read-only placeholder' and 'missing functionality' gap from the
QA audit is now resolved:

COURSES — categories/instructors/locations can now be deleted:
- Added update/delete methods to course-reference-data.service.ts
- Added deleteCategory/deleteInstructor/deleteLocation server actions
- Created DeleteRefDataButton client component with confirmation dialog
- Wired delete buttons into all three table pages

BOOKINGS — calendar month navigation now works:
- Calendar was hardcoded to current month with disabled prev/next
- Added year/month search params for server-side month rendering
- Replaced disabled buttons with Link-based navigation
- Verified: clicking next/prev correctly renders different months

DOCUMENTS — templates page now reads from database:
- Was hardcoded empty array; now queries document_templates table
- Table exists since migration 20260414000006_shared_templates.sql

FISCHEREI — statistics page shows real data:
- Replaced dashed-border placeholder with 6 real stat cards
- Queries waters, species, stocking, catch_books, leases, permits
- Shows counts + stocking costs + pending catch books
- Falls back to helpful message when no data exists

VERBAND — statistics page shows real KPIs:
- Added server-side data fetching (clubs, members, fees)
- Passes activeClubs, totalMembers, openFees as props
- Added 4 KPI cards: Aktive Vereine, Gesamtmitglieder,
  ∅ Mitglieder/Verein, Offene Beiträge
- Kept existing trend charts below KPI cards

apps/web/app/[locale]/home/[account]/bookings/calendar/page.tsx

@@ -14,6 +14,7 @@ import { CmsPageShell } from '~/components/cms-page-shell';
 
 interface PageProps {
   params: Promise<{ account: string }>;
+  searchParams: Promise<Record<string, string | string[] | undefined>>;
 }
 
 const WEEKDAYS = ['Mo', 'Di', 'Mi', 'Do', 'Fr', 'Sa', 'So'];
@@ -51,8 +52,9 @@ function isDateInRange(
   return date >= checkIn && date < checkOut;
 }
 
-export default async function BookingCalendarPage({ params }: PageProps) {
+export default async function BookingCalendarPage({ params, searchParams }: PageProps) {
   const { account } = await params;
+  const search = await searchParams;
   const t = await getTranslations('bookings');
   const client = getSupabaseServerClient();
 
@@ -73,8 +75,15 @@ export default async function BookingCalendarPage({ params }: PageProps) {
   const api = createBookingManagementApi(client);
 
   const now = new Date();
-  const year = now.getFullYear();
-  const month = now.getMonth();
+  const year = Number(search.year) || now.getFullYear();
+  const month = search.month != null ? Number(search.month) - 1 : now.getMonth();
+
+  // Compute prev/next month for navigation links
+  const prevMonth = month === 0 ? 12 : month;
+  const prevYear = month === 0 ? year - 1 : year;
+  const nextMonth = month === 11 ? 1 : month + 2;
+  const nextYear = month === 11 ? year + 1 : year;
+
   const daysInMonth = getDaysInMonth(year, month);
   const firstWeekday = getFirstWeekday(year, month);
 
@@ -160,10 +169,12 @@ export default async function BookingCalendarPage({ params }: PageProps) {
               <Button
                 variant="ghost"
                 size="icon"
-                disabled
+                asChild
                 aria-label={t('calendar.previousMonth')}
               >
-                <ChevronLeft className="h-4 w-4" aria-hidden="true" />
+                <Link href={`/home/${account}/bookings/calendar?year=${prevYear}&month=${prevMonth}`}>
+                  <ChevronLeft className="h-4 w-4" aria-hidden="true" />
+                </Link>
               </Button>
               <CardTitle>
                 {MONTH_NAMES[month]} {year}
@@ -171,10 +182,12 @@ export default async function BookingCalendarPage({ params }: PageProps) {
               <Button
                 variant="ghost"
                 size="icon"
-                disabled
+                asChild
                 aria-label={t('calendar.nextMonth')}
               >
-                <ChevronRight className="h-4 w-4" aria-hidden="true" />
+                <Link href={`/home/${account}/bookings/calendar?year=${nextYear}&month=${nextMonth}`}>
+                  <ChevronRight className="h-4 w-4" aria-hidden="true" />
+                </Link>
               </Button>
             </div>
           </CardHeader>