fix(FN-1162): keep mobile file browser header controls accessible

- Update file browser header styles to wrap cleanly on small screens and preserve readable truncated labels
- Increase mobile close-button hit area and keep close action visible within header actions layout
- Add responsive WorkspaceSelector constraints to prevent menu/trigger overflow on narrow viewports
- Add a regression test that verifies the mobile close button remains visible and clickable

packages/dashboard/app/components/FileBrowserModal.test.tsx

@@ -145,6 +145,33 @@ describe("FileBrowserModal", () => {
     });
   });
 
+  it("keeps mobile close button visible and clickable", async () => {
+    Object.defineProperty(window, "innerWidth", {
+      writable: true,
+      configurable: true,
+      value: 375,
+    });
+
+    const { container } = render(
+      <FileBrowserModal
+        initialWorkspace="project"
+        isOpen={true}
+        onClose={mockOnClose}
+      />,
+    );
+
+    fireEvent(window, new Event("resize"));
+
+    const closeButton = container.querySelector("button.modal-close");
+    expect(closeButton).toBeInTheDocument();
+    expect(closeButton).toBeVisible();
+
+    fireEvent.click(closeButton!);
+    await waitFor(() => {
+      expect(mockOnClose).toHaveBeenCalledTimes(1);
+    });
+  });
+
   it("closes on Escape and saves on Cmd+S", () => {
     mockUseWorkspaceFileEditor.mockReturnValue({
       ...defaultEditorState,

packages/dashboard/app/components/WorkspaceSelector.css

@@ -109,3 +109,21 @@
   font-size: 11px;
   color: var(--text-muted);
 }
+
+@media (max-width: 768px) {
+  .workspace-selector-trigger {
+    min-width: 0;
+    max-width: min(56vw, 160px);
+  }
+
+  .workspace-selector-menu {
+    left: auto;
+    right: 0;
+    min-width: min(300px, calc(100vw - 24px));
+    max-width: calc(100vw - 24px);
+  }
+
+  .workspace-selector-option-meta {
+    max-width: 120px;
+  }
+}