Expand spec coverage for DownloadService, CodeEditorComponent, and AnnotationSuggestionComponent

[aglinxinyuan]

Task Summary

Three areas under-tested in the current frontend spec suite:

Target	Today	Why under-tested
DownloadService	8 active it.skip(...) blocks	All written against the Jasmine done() / fail() callback shape, which the vitest runner doesn't accept (#4861).
CodeEditorComponent	a single should create smoke test	Most of the component's behaviour (operator-type → language detection, language-title formatting, coeditor cursor styles) goes untested.
AnnotationSuggestionComponent	no spec at all	The two @Output() event emitters are unverified.

Plan

• DownloadService: rewrite the eight it.skip(...) blocks with firstValueFrom / await expect(...).rejects.toThrow(...) against the same mocks, then add new cases for downloadWorkflow, downloadOperatorsResult (single-file path), getWorkflowResultDownloadability, default-filename fallback, and isLogin=false plumbing.
• CodeEditorComponent: add language-detection cases for the three V2 Python operator types + Java + unknown, assert languageTitle formatting, and exercise getCoeditorCursorStyles for valid clientId / colour shapes.
• AnnotationSuggestionComponent: new spec file. Cover input defaults, accept / decline event emission, and that the two emitters are independent.

Both branches under active development (main and the chore/monaco-lsp-v10 v10 upgrade in #4997) should run the new specs to completion.

Verification plan

• yarn test on main — all new specs pass
• yarn test on chore/monaco-lsp-v10 — same specs pass against the v10-rewritten editor / debugger code
• No existing specs regress

Task Type

• Testing / QA