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

packages/features/course-management/src/components/delete-ref-data-button.tsx

@@ -0,0 +1,113 @@
+'use client';
+
+import { useAction } from 'next-safe-action/hooks';
+import { useRouter } from 'next/navigation';
+import { useState } from 'react';
+
+import { Loader2, Trash2 } from 'lucide-react';
+
+import {
+  AlertDialog,
+  AlertDialogAction,
+  AlertDialogCancel,
+  AlertDialogContent,
+  AlertDialogDescription,
+  AlertDialogFooter,
+  AlertDialogHeader,
+  AlertDialogTitle,
+  AlertDialogTrigger,
+} from '@kit/ui/alert-dialog';
+import { Button } from '@kit/ui/button';
+import { toast } from '@kit/ui/sonner';
+
+import {
+  deleteCategory,
+  deleteInstructor,
+  deleteLocation,
+} from '../server/actions/course-actions';
+
+type RefDataType = 'category' | 'instructor' | 'location';
+
+const actions = {
+  category: deleteCategory,
+  instructor: deleteInstructor,
+  location: deleteLocation,
+};
+
+const labels: Record<RefDataType, { name: string; confirm: string }> = {
+  category: {
+    name: 'Kategorie',
+    confirm: 'Möchten Sie diese Kategorie wirklich löschen?',
+  },
+  instructor: {
+    name: 'Kursleiter',
+    confirm: 'Möchten Sie diesen Kursleiter wirklich löschen?',
+  },
+  location: {
+    name: 'Standort',
+    confirm: 'Möchten Sie diesen Standort wirklich löschen?',
+  },
+};
+
+interface DeleteRefDataButtonProps {
+  id: string;
+  type: RefDataType;
+  itemName: string;
+}
+
+export function DeleteRefDataButton({
+  id,
+  type,
+  itemName,
+}: DeleteRefDataButtonProps) {
+  const router = useRouter();
+  const label = labels[type];
+  const action = useAction(actions[type], {
+    onSuccess: () => {
+      toast.success(`${label.name} „${itemName}" gelöscht`);
+      router.refresh();
+    },
+    onError: () =>
+      toast.error(`Fehler beim Löschen`, {
+        description:
+          'Möglicherweise wird der Eintrag noch von Kursen verwendet.',
+      }),
+  });
+
+  return (
+    <AlertDialog>
+      <AlertDialogTrigger asChild>
+        <Button
+          variant="ghost"
+          size="icon"
+          className="text-destructive hover:text-destructive hover:bg-destructive/10 h-8 w-8"
+          aria-label={`${label.name} löschen`}
+        >
+          <Trash2 className="h-4 w-4" />
+        </Button>
+      </AlertDialogTrigger>
+      <AlertDialogContent>
+        <AlertDialogHeader>
+          <AlertDialogTitle>{label.name} löschen</AlertDialogTitle>
+          <AlertDialogDescription>
+            {label.confirm} „<strong>{itemName}</strong>" wird unwiderruflich
+            entfernt.
+          </AlertDialogDescription>
+        </AlertDialogHeader>
+        <AlertDialogFooter>
+          <AlertDialogCancel>Abbrechen</AlertDialogCancel>
+          <AlertDialogAction
+            onClick={() => action.execute({ id })}
+            disabled={action.isPending}
+            className="bg-destructive text-destructive-foreground hover:bg-destructive/90"
+          >
+            {action.isPending && (
+              <Loader2 className="mr-2 h-4 w-4 animate-spin" />
+            )}
+            Löschen
+          </AlertDialogAction>
+        </AlertDialogFooter>
+      </AlertDialogContent>
+    </AlertDialog>
+  );
+}

packages/features/course-management/src/components/index.ts

@@ -1,2 +1,3 @@
 export { CreateCourseForm } from './create-course-form';
 export { EnrollParticipantDialog } from './enroll-participant-dialog';
+export { DeleteRefDataButton } from './delete-ref-data-button';

packages/features/course-management/src/server/actions/course-actions.ts

@@ -188,3 +188,32 @@ export const createSession = authActionClient
     logger.info({ name: 'course.createSession' }, 'Session created');
     return { success: true, data: result };
   });
+
+// ── Delete reference data ──
+
+export const deleteCategory = authActionClient
+  .inputSchema(z.object({ id: z.string().uuid() }))
+  .action(async ({ parsedInput: { id } }) => {
+    const client = getSupabaseServerClient();
+    const api = createCourseManagementApi(client);
+    await api.referenceData.deleteCategory(id);
+    return { success: true };
+  });
+
+export const deleteInstructor = authActionClient
+  .inputSchema(z.object({ id: z.string().uuid() }))
+  .action(async ({ parsedInput: { id } }) => {
+    const client = getSupabaseServerClient();
+    const api = createCourseManagementApi(client);
+    await api.referenceData.deleteInstructor(id);
+    return { success: true };
+  });
+
+export const deleteLocation = authActionClient
+  .inputSchema(z.object({ id: z.string().uuid() }))
+  .action(async ({ parsedInput: { id } }) => {
+    const client = getSupabaseServerClient();
+    const api = createCourseManagementApi(client);
+    await api.referenceData.deleteLocation(id);
+    return { success: true };
+  });

packages/features/course-management/src/server/services/course-reference-data.service.ts

@@ -104,5 +104,80 @@ export function createCourseReferenceDataService(
       if (error) throw error;
       return data;
     },
+
+    // ── Update / Delete ──
+
+    async updateCategory(
+      id: string,
+      input: { name?: string; description?: string },
+    ) {
+      const { error } = await client
+        .from('course_categories')
+        .update(input)
+        .eq('id', id);
+      if (error) throw error;
+    },
+
+    async deleteCategory(id: string) {
+      const { error } = await client
+        .from('course_categories')
+        .delete()
+        .eq('id', id);
+      if (error) throw error;
+    },
+
+    async updateInstructor(
+      id: string,
+      input: {
+        firstName?: string;
+        lastName?: string;
+        email?: string;
+        phone?: string;
+        qualifications?: string;
+        hourlyRate?: number;
+      },
+    ) {
+      const update: Record<string, unknown> = {};
+      if (input.firstName !== undefined) update.first_name = input.firstName;
+      if (input.lastName !== undefined) update.last_name = input.lastName;
+      if (input.email !== undefined) update.email = input.email;
+      if (input.phone !== undefined) update.phone = input.phone;
+      if (input.qualifications !== undefined)
+        update.qualifications = input.qualifications;
+      if (input.hourlyRate !== undefined) update.hourly_rate = input.hourlyRate;
+
+      const { error } = await client
+        .from('course_instructors')
+        .update(update)
+        .eq('id', id);
+      if (error) throw error;
+    },
+
+    async deleteInstructor(id: string) {
+      const { error } = await client
+        .from('course_instructors')
+        .delete()
+        .eq('id', id);
+      if (error) throw error;
+    },
+
+    async updateLocation(
+      id: string,
+      input: { name?: string; address?: string; room?: string; capacity?: number },
+    ) {
+      const { error } = await client
+        .from('course_locations')
+        .update(input)
+        .eq('id', id);
+      if (error) throw error;
+    },
+
+    async deleteLocation(id: string) {
+      const { error } = await client
+        .from('course_locations')
+        .delete()
+        .eq('id', id);
+      if (error) throw error;
+    },
   };
 }