Summary

• add stable test/accessibility hooks to CodeMirror-backed editors and affected tool panes
• fix read-only highlighted output panes so they mount while empty and update when output arrives
• update end-user E2E specs to use shared editor helpers instead of raw textarea selectors
• add accessible Barcode layout toggle labeling and disable empty Data Generator copy icon

Verification

• cd frontend && bun run format
• cd frontend && node_modules/@playwright/test/cli.js test e2e/codeEncoder.spec.js e2e/codeConverter.spec.js e2e/hashGenerator.spec.js e2e/codeEncrypter.spec.js e2e/textUtilities.spec.js e2e/textDiffChecker.spec.js e2e/jwtDebugger.spec.js e2e/codeFormatter.spec.js e2e/dataGenerator.spec.js e2e/barcodeGenerator.spec.js e2e/regExpTester.spec.js (138 passed)
• cd frontend && node_modules/@playwright/test/cli.js test (217 passed)
• cd frontend && node_modules/vitest/vitest.mjs run (31 passed)
• cd frontend && node_modules/vite/bin/vite.js build --mode production
• go test ./internal/... ./service/... ./pkg/...

Known unrelated issue

• go test ./... still fails in cmd/testserver because cmd/testserver/main.go references service.NewConversionService, which is not part of this change.