Adds the Offerings module and retargets the CI/CD pipeline to Api.SlpSoftware

Implements Unit 2 "Offerings" (backend module, admin CRUD UI with
drag-and-drop reordering, public GET /api/v1/offerings endpoint) and
executes the feature's D-15 CI/CD cutover, switching the deploy
pipeline's build/publish target from SlpModularCms.Api to
SlpModularCms.Api.SlpSoftware.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FWyStNL2ZsjrS7FLd7xvvN

frontend/src/features/offerings/hooks/useOfferingsDnd.ts

@@ -0,0 +1,53 @@
+import { useState } from 'react';
+import {
+    PointerSensor,
+    KeyboardSensor,
+    useSensor,
+    useSensors,
+    type DragStartEvent,
+    type DragEndEvent,
+} from '@dnd-kit/core';
+import { arrayMove, sortableKeyboardCoordinates } from '@dnd-kit/sortable';
+import { useReorderOfferings } from '../services/useReorderOfferings';
+import type { OfferingAdminDto } from '../services/types';
+
+export function useOfferingsDnd(offerings: OfferingAdminDto[]) {
+    const [items, setItems] = useState(offerings);
+    const [syncedOfferings, setSyncedOfferings] = useState(offerings);
+    const [activeId, setActiveId] = useState<string | null>(null);
+    const reorderMutation = useReorderOfferings();
+
+    // Adjusting state during render (not in an effect) avoids the extra render pass
+    // an effect-based sync would cause — see https://react.dev/learn/you-might-not-need-an-effect.
+    if (offerings !== syncedOfferings) {
+        setSyncedOfferings(offerings);
+        setItems(offerings);
+    }
+
+    const sensors = useSensors(
+        useSensor(PointerSensor),
+        useSensor(KeyboardSensor, { coordinateGetter: sortableKeyboardCoordinates }),
+    );
+
+    function handleDragStart(event: DragStartEvent) {
+        setActiveId(event.active.id as string);
+    }
+
+    function handleDragEnd(event: DragEndEvent) {
+        setActiveId(null);
+        const { active, over } = event;
+        if (over === null || active.id === over.id) return;
+
+        const oldIndex = items.findIndex((item) => item.id === active.id);
+        const newIndex = items.findIndex((item) => item.id === over.id);
+        if (oldIndex === -1 || newIndex === -1) return;
+
+        const reordered = arrayMove(items, oldIndex, newIndex);
+        setItems(reordered);
+        reorderMutation.mutate(reordered.map((item) => item.id));
+    }
+
+    const activeItem = activeId === null ? null : (items.find((item) => item.id === activeId) ?? null);
+
+    return { items, sensors, activeItem, handleDragStart, handleDragEnd };
+}