Fix editorial app-surface overflow polish

[jaeyunha]

Closes #384

Summary

• salvage from completed visible lane: themed scrollbars, inbox pane width/overflow, dense type utilities, toned selected states

Verification / blocker

• make check ✅
• make test terminated / focused DB tests blocked because database exponential did not exist
• make test-e2e ❌ baseline/auth setup blocker: /api/test/create-session 404 and callback URL mismatch
• Ever blocked: extension not connected / banner-only

QA_BLOCKED: preserved after prior push auth failure; needs fresh visual/browser/controller acceptance before merge.