FN-7659: paginate and sort the Archived column newest-first

Adds server-side pagination for the Archived task column, sorted by most-recently-archived first, with a Show more control on the dashboard.

- Add ArchiveDatabase.listPage and TaskStore.listArchivedTasks for a bounded SQL LIMIT/OFFSET read ordered by archivedAt DESC
- Add GET /tasks/archived route for paged archive fetches, leaving the legacy merged listTasks({includeArchived}) path unchanged
- Wire useTasks.loadArchivedTasks to fetch page 1 on first Archived-column expand and loadMoreArchivedTasks for subsequent pages
- Add a "Show more" affordance in Column.tsx/Board.tsx/MainContent.tsx to trigger loading additional archived pages
- Extend taskSorting.ts to keep archived task ordering stable with the new paged data
- Add core and dashboard tests covering archive pagination and store/route behavior
- Add changeset for @runfusion/fusion (minor) and update docs/storage.md and docs/dashboard-guide.md

Files changed:
 .changeset/FN-7659-archived-pagination.md          |   7 +
 docs/dashboard-guide.md                            |   4 +-
 docs/storage.md                                    |   7 +
 packages/core/src/__tests__/archive-db-pagination.test.ts    |  94 ++++++++
 packages/core/src/__tests__/store-archive-search.test.ts     |  63 ++++++
 packages/core/src/archive-db.ts                    |  18 ++
 packages/core/src/store.ts                         |  32 +++
 packages/dashboard/app/App.tsx                     |   5 +-
 packages/dashboard/app/api/legacy.ts               |  19 ++
 packages/dashboard/app/components/Board.tsx        |  19 +-
 packages/dashboard/app/components/Column.tsx       |  48 ++++-
 packages/dashboard/app/components/__tests__/Column.test.tsx       |  41 ++++
 packages/dashboard/app/components/__tests__/taskSorting.test.ts   |  27 +++
 packages/dashboard/app/components/dashboard/MainContent.tsx       |   9 +
 packages/dashboard/app/components/dashboard/types.ts    |   6 +
 packages/dashboard/app/components/taskSorting.ts   |  16 ++
 packages/dashboard/app/hooks/__tests__/useTasks.test.ts | 236 ++++++++++++++++++++-
 packages/dashboard/app/hooks/useTasks.ts           | 173 ++++++++++++++-
 packages/dashboard/app/test/mockApi.ts             |   3 +
 packages/dashboard/src/routes/__tests__/tasks-archived-pagination.test.ts |  94 ++++++++
 packages/dashboard/src/routes/register-task-workflow-routes.ts  |  32 +++
 21 files changed, 930 insertions(+), 23 deletions(-)

Fusion-Task-Id: FN-7659

Fusion-Task-Lineage: 7a5a1f62-277c-4f29-883c-62e75b269bc5

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

packages/dashboard/app/api/legacy.ts

@@ -299,6 +299,25 @@ export function fetchTasks(
   return api<Task[]>(`/tasks${suffix}`);
 }
 
+/**
+ * FNXC:ArchivePagination 2026-07-08-00:00:
+ * Dedicated paged read for the Archived board column (FN-7659). Returns
+ * one bounded page (default 100) ordered `archivedAt DESC` plus `total`/
+ * `hasMore` so the caller can drive a "Show more" affordance without ever
+ * fetching the whole archive in one request.
+ */
+export function fetchArchivedTasks(
+  projectId?: string,
+  limit?: number,
+  offset?: number,
+): Promise<{ tasks: Task[]; total: number; hasMore: boolean }> {
+  const search = new URLSearchParams();
+  if (limit !== undefined) search.set("limit", String(limit));
+  if (offset !== undefined) search.set("offset", String(offset));
+  const suffix = search.size > 0 ? `?${search.toString()}` : "";
+  return api<{ tasks: Task[]; total: number; hasMore: boolean }>(withProjectId(`/tasks/archived${suffix}`, projectId));
+}
+
 export async function fetchTaskDetail(id: string, projectId?: string): Promise<TaskDetail> {
   const maxAttempts = 2; // 1 initial + 1 retry
   const url = buildApiUrl(withProjectId(`/tasks/${id}`, projectId));