feat(files): add Files page with nav, list, details, upload, and routing

Creates the full Files page UI (Tasks 8 & 9): FilesNav, FileListItem,
FileList, FileDetails, FileUploadArea components, FilesPage layout, and
wires up the /files route plus sidebar/mobile-nav entries.

apps/web/src/components/layout/sidebar.tsx

@@ -3,10 +3,10 @@ import { cn } from "@/lib/utils";
 import {
   LayoutGrid,
   Workflow,
-  FolderOpen,
   HelpCircle,
   Settings,
   Grid3x3,
+  FolderOpen,
 } from "lucide-react";
 import type { LucideIcon } from "lucide-react";