✅(frontend) mock saxen in jest config

ui-kit 0.28.0 pulls in read-excel-file, whose CommonJS build requires
saxen, an ESM-only package that jest cannot parse. No unit test parses
spreadsheets, so a stub parser is enough, following the pretty-bytes
precedent.

src/frontend/apps/drive/__mocks__/saxen.js

@@ -0,0 +1,10 @@
+// saxen is ESM-only, which Jest cannot parse from read-excel-file's CJS
+// build (pulled in by ui-kit). No unit test parses spreadsheets, so a
+// stub Parser is enough.
+module.exports = {
+  Parser: class Parser {
+    on() {}
+    parse() {}
+    stop() {}
+  },
+};

src/frontend/apps/drive/jest.config.ts

@@ -12,6 +12,7 @@ const config: Config = {
     "\\.(css|less|scss|sass|svg|png|jpg|jpeg|gif)$":
       "<rootDir>/__mocks__/fileMock.js",
     "^pretty-bytes$": "<rootDir>/__mocks__/pretty-bytes.js",
+    "^saxen$": "<rootDir>/__mocks__/saxen.js",
     // Then handle path aliases
     ...pathsToModuleNameMapper(tsconfig.compilerOptions.paths || {}, {
       prefix: "<rootDir>/",