feat(workspace): trash for notes

Deleting a note (or its folder) moves it to the trash instead of erasing
it. Trashed notes leave the tree, search, export and stats and are hidden
from everyone they were shared with; the owner sees them read-only with a
restore banner. New endpoints list, restore, purge and empty the trash;
restoring recreates a deleted folder. Sidebar entry and mobile menu item
with counter, list view with two-tap permanent delete.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/lib/api.ts

@@ -3,6 +3,7 @@ import {
   AuthStatus,
   DashboardStats,
   Document,
+  TrashedDocument,
   DocumentBlock,
   DocShare,
   KanbanColumn,
@@ -647,10 +648,27 @@ export const api = {
     });
   },
 
+  /** Moves the note to the trash (owner) or leaves a shared note (others). */
   async deleteDocument(id: string): Promise<void> {
     await request(`/api/v1/documents/${id}`, { method: 'DELETE' });
   },
 
+  async getTrash(): Promise<TrashedDocument[]> {
+    return request<TrashedDocument[]>('/api/v1/documents/trash');
+  },
+
+  async restoreDocument(id: string): Promise<void> {
+    await request(`/api/v1/documents/${id}/restore`, { method: 'POST' });
+  },
+
+  async purgeDocument(id: string): Promise<void> {
+    await request(`/api/v1/documents/${id}/permanent`, { method: 'DELETE' });
+  },
+
+  async emptyTrash(): Promise<{ deleted: number }> {
+    return request<{ deleted: number }>('/api/v1/documents/trash', { method: 'DELETE' });
+  },
+
   async moveDocument(id: string, folderPath: string): Promise<Document> {
     const d = await request<Document>(`/api/v1/documents/${id}/move`, {
       method: 'PUT',