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/pages/files-page.tsx

@@ -0,0 +1,25 @@
+import { AppLayout } from "@/components/layout/app-layout";
+import { FilesNav } from "@/components/files/files-nav";
+import { FileList } from "@/components/files/file-list";
+import { FileDetails } from "@/components/files/file-details";
+import { FileUploadArea } from "@/components/files/file-upload-area";
+import { useFilesPageStore } from "@/stores/files-page-store";
+
+export function FilesPage() {
+  const { activeTab } = useFilesPageStore();
+  return (
+    <AppLayout showToolPanel={false}>
+      <div className="flex h-full w-full overflow-hidden">
+        <FilesNav />
+        {activeTab === "recent" ? (
+          <>
+            <FileList />
+            <FileDetails />
+          </>
+        ) : (
+          <FileUploadArea />
+        )}
+      </div>
+    </AppLayout>
+  );
+}