fix(a11y): reconcile responsive layouts and multilingual UI

flake.nix

@@ -16,9 +16,10 @@
         function: nixpkgs.lib.genAttrs supportedSystems (system: function nixpkgs.legacyPackages.${system});
     in
     {
-      devShells = forAllSystems (pkgs: {
-        default = pkgs.mkShell {
-          packages = with pkgs; [
+      devShells = forAllSystems (
+        pkgs:
+        let
+          developmentPackages = with pkgs; [
             nodejs_24
             git
             curl
@@ -27,8 +28,35 @@
             fd
             python3
           ];
-        };
-      });
+        in
+        {
+          default = pkgs.mkShell { packages = developmentPackages; };
+        }
+        // pkgs.lib.optionalAttrs pkgs.stdenv.hostPlatform.isLinux {
+          # Keep driver and browser revisions paired through the existing lockfile.
+          # Opt-in so ordinary content editing does not require browser downloads.
+          browser = pkgs.mkShell {
+            packages = developmentPackages ++ [ pkgs.playwright-driver ];
+            PLAYWRIGHT_MODULE = "${pkgs.playwright-driver}/index.mjs";
+            PLAYWRIGHT_BROWSERS_PATH = pkgs.playwright-driver.selectBrowsers {
+              withFirefox = false;
+              withWebkit = false;
+              withFfmpeg = false;
+            };
+            PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD = "1";
+            # Nix supplies browser libraries via patched runtime paths, not apt.
+            PLAYWRIGHT_SKIP_VALIDATE_HOST_REQUIREMENTS = "true";
+            FONTCONFIG_FILE = pkgs.makeFontsConf {
+              fontDirectories = with pkgs; [
+                dejavu_fonts
+                liberation_ttf
+                noto-fonts
+              ];
+            };
+            ASTRO_TELEMETRY_DISABLED = "1";
+          };
+        }
+      );
 
       formatter = forAllSystems (pkgs: pkgs.nixfmt);
     };