chore: evaluate jsdom v28 major upgrade

[corvid-agent]

Summary

The project currently pins jsdom at ^27.1.0 (resolved to 27.4.0). jsdom v28 is available but includes breaking changes that need evaluation.

Risk assessment

jsdom v28 change	Affected area	Risk
CustomEvent constructor behavior	shell.spec.ts (dispatches new Event('resize'))	Low
Stricter localStorage mock	github.service.spec.ts (uses vi.stubGlobal)	Low
document.createElement stricter validation	editor-page-computed.spec.ts (spies on origCreateElement)	Medium
FormData / File constructor changes	Not used in unit tests	None

Recommended steps

1. Pin jsdom more tightly to ~27.4.0 to prevent accidental major upgrade via transitive deps
2. Create a test branch with jsdom@^28.1.0 and run the full suite
3. Fix any failures before merging
4. Consider adding overrides/resolutions block to prevent nested packages from pulling v28 prematurely