feat(radar): Add empty state illustrations when no eligible issues are found

## Description Currently, when the Radar page finds zero eligible issues, it just shows a plain text message: `No eligible issues found matching your criteria.` We want to improve this experience by adding a subtle, technical empty state graphic or layout. ## Requirements - Do NOT use generic 'cute' illustrations. Keep it aligned with our 'Light. Precise. Technical.' design philosophy. - Consider a clean ASCII-style graphic, a wireframe diagram, or a minimal Lucide icon layout. - Suggest adjusting search criteria within the empty state text. This is a perfect issue for a frontend developer with an eye for minimal, technical design!