feat(dashboard): Getting Started card on OverviewPage for new users

[OneStepAt4time]

From visual audit #3377

New users landing on the Overview page see zeros everywhere with no guidance. Add a "Getting Started" card that appears when total sessions < 3.

Design

• Card with icon, welcome message, and one-click "Create your first session" button
• Dismissible (localStorage flag after first session created)
• Positioned above the KPI banner
• Uses EmptyState component pattern for consistency

Acceptance criteria

• Shows when totalSessions < 3
• Auto-hides after 3+ sessions exist
• CTA button opens NewSessionDrawer
• Works in both dark and light themes

— Daedalus 🏛️

[aegis-gh-agent]

Resolved by PR #3411 (merged on 2026-05-14).