feat(FN-4149): normalize mobile toolbar sizing and add touch target coverag

Added test coverage for mobile toolbar touch target CSS and normalized mobile toolbar sizing in the FileBrowser component.

Fusion-Task-Id: FN-4149

packages/dashboard/app/components/FileBrowser.css

@@ -390,7 +390,7 @@
   }
 
   .file-editor-toolbar {
-    align-items: flex-start;
+    align-items: center;
   }
 
   .file-editor-toolbar-actions {
@@ -400,6 +400,7 @@
 
   .file-editor-toolbar-actions .btn {
     min-height: var(--mobile-nav-height);
+    min-width: var(--mobile-nav-height);
   }
 
   .file-browser-modal-header .modal-close {

packages/dashboard/app/components/__tests__/FileEditor.test.tsx

@@ -1,5 +1,6 @@
 import { describe, it, expect, vi } from "vitest";
 import { render, screen, fireEvent } from "@testing-library/react";
+import { loadAllAppCss } from "../../test/cssFixture";
 import { FileEditor } from "../FileEditor";
 
 describe("FileEditor", () => {
@@ -344,6 +345,37 @@ describe("FileEditor", () => {
     });
   });
 
+  describe("mobile toolbar CSS", () => {
+    it("keeps file editor toolbar action buttons at a shared mobile touch target size", () => {
+      const css = loadAllAppCss();
+      const selectorIndex = css.indexOf(".file-editor-toolbar-actions .btn");
+
+      expect(selectorIndex).toBeGreaterThanOrEqual(0);
+
+      const mediaIndex = css.lastIndexOf("@media (max-width: 768px)", selectorIndex);
+      expect(mediaIndex).toBeGreaterThanOrEqual(0);
+
+      const openBraceIndex = css.indexOf("{", mediaIndex);
+      let depth = 1;
+      let cursor = openBraceIndex + 1;
+
+      while (cursor < css.length && depth > 0) {
+        if (css[cursor] === "{") {
+          depth += 1;
+        } else if (css[cursor] === "}") {
+          depth -= 1;
+        }
+        cursor += 1;
+      }
+
+      const mobileCss = css.slice(openBraceIndex + 1, cursor - 1);
+
+      expect(mobileCss).toMatch(
+        /\.file-editor-toolbar-actions\s+\.btn\s*\{[^}]*min-height:\s*var\(--mobile-nav-height\);[^}]*min-width:\s*var\(--mobile-nav-height\);[^}]*\}/,
+      );
+    });
+  });
+
   describe("markdown preview scrollability", () => {
     it("preview container has correct CSS classes for scrolling", () => {
       render(<FileEditor content="# Hello World" onChange={vi.fn()} filePath="readme.md" />);