refactor: extract draft task styles

[alteixeira20]

Summary

• extract draft-task styles into a dedicated workspace stylesheet
• reduce responsibility in the existing task-row stylesheet
• preserve selector behavior, cascade order, responsive rules, and UI contracts

Validation

• 35 frontend test files passed
• 357 frontend tests passed
• frontend lint passed
• frontend typecheck passed
• Next.js production build passed
• API lint passed
• 211 API tests passed
• Alembic reported no new upgrade operations
• git diff check passed

Roadmap

Implements the code-bearing portion of RF-106.

Browser screenshot comparison remains deferred to the consolidated final manual QA pass.