feat(search): per-source load-more pagination in Search.vue (#115 frontend)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/views/searchPagination.ts

@@ -0,0 +1,46 @@
+// Pure pagination helpers for Search.vue "加载更多" (load-more) per source + tab.
+// Kept framework-free so root vitest can unit-cover the logic (see searchPagination.test.ts).
+
+/** Minimal shape shared by songs / albums / playlists: needs a stable dedup key. */
+export interface Keyed {
+  id: string;
+  platform: string;
+}
+
+/** Stable dedup key for a result item: `${platform}:${id}`. */
+export function itemKey(item: Keyed): string {
+  return `${item.platform}:${item.id}`;
+}
+
+/**
+ * Merge `incoming` into `existing`, deduped by `${platform}:${id}`.
+ * Order is preserved with existing items first; incoming items already present
+ * (or duplicated within the incoming batch) are dropped.
+ */
+export function mergeDedup<T extends Keyed>(existing: T[], incoming: T[]): T[] {
+  const seen = new Set<string>(existing.map(itemKey));
+  const result = existing.slice();
+  for (const item of incoming) {
+    const key = itemKey(item);
+    if (seen.has(key)) continue;
+    seen.add(key);
+    result.push(item);
+  }
+  return result;
+}
+
+/**
+ * Whether another page might exist: a full page (=== pageSize) means keep the
+ * button; a short/empty page (< pageSize) means the source is exhausted.
+ */
+export function hasMore(returnedCount: number, pageSize: number): boolean {
+  return returnedCount >= pageSize;
+}
+
+/**
+ * Offset for the next page request. Offsets are page-aligned, so this is simply
+ * the number of items already shown for that source+type.
+ */
+export function nextOffset(currentCountForSource: number, pageSize: number): number {
+  return Math.ceil(currentCountForSource / pageSize) * pageSize;
+}