chore(documents): remove legacy /documents/files route + folder tree

The /documents/files page rendered a storagePath-prefix folder tree
disconnected from document_folders. Replaced by the unified hub
(Task 15). 301 redirect catches stray bookmarks. file-browser-store
repurposed to hold the document_folders.id selection.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/layout/sidebar.tsx

@@ -13,7 +13,6 @@ import {
   Building2,
   Receipt,
   FileText,
-  FolderOpen,
   Bell,
   Camera,
   Globe,
@@ -116,10 +115,7 @@ function buildNavSections(portSlug: string | undefined): NavSection[] {
     {
       title: 'Documents',
       marinaRequired: true,
-      items: [
-        { href: `${base}/documents`, label: 'Documents', icon: FileText },
-        { href: `${base}/documents/files`, label: 'Files', icon: FolderOpen },
-      ],
+      items: [{ href: `${base}/documents`, label: 'Documents', icon: FileText }],
     },
     {
       title: 'Financial',