fix(views): wrap My Files table for mobile horizontal scroll

The table at /files was wider than the viewport on iPhone-class widths
(~375 px) — the rightmost column with the Copy and Delete buttons clipped
off-screen with no scroll affordance. Wrapping the table in a
.table-wrap div with overflow-x: auto lets the table scroll within
itself; moving the outer border to the wrapper preserves the desktop
visual unchanged.

- public/style.css: add .table-wrap rule, move border off table, add
  min-width: 100% so the table still fills wide viewports.
- src/views/file-list.ts: wrap <table> in <div class="table-wrap">.
- tests/integration/pages.test.ts: assert rendered HTML contains
  class="table-wrap".

src/views/file-list.ts

@@ -24,14 +24,16 @@ export function fileListPage(files: FileRow[], baseUrl: string): string {
   return layout('My files', `
     <h1>My files</h1>
     <p><a href="/upload">Upload new file</a></p>
-    <table>
-      <thead>
-        <tr>
-          <th>Name</th><th>Type</th><th>Size</th><th>Uploaded</th><th></th>
-        </tr>
-      </thead>
-      <tbody>${rows}</tbody>
-    </table>
+    <div class="table-wrap">
+      <table>
+        <thead>
+          <tr>
+            <th>Name</th><th>Type</th><th>Size</th><th>Uploaded</th><th></th>
+          </tr>
+        </thead>
+        <tbody>${rows}</tbody>
+      </table>
+    </div>
   `, { authed: true });
 }