feat(ui): build dashboard with readiness overview and trends

[leoneperdigao]

Description

Build the main dashboard view that gives stakeholders an at-a-glance view of their organization's quantum readiness. This is the landing page of the application and should communicate readiness status, trends, and areas requiring attention.

Tasks

• Implement organization readiness score gauge chart (0-100, color-coded)
• Build trend chart showing readiness score over the past 6 and 12 months
• Add breakdown cards by algorithm type (RSA, ECC, AES, SHA counts)
• Add breakdown by severity (critical, high, medium, low)
• Add breakdown by status (vulnerable, in-progress, migrated, accepted-risk)
• Create "Top 10 Most Vulnerable" panel for repositories and endpoints
• Build recent scan activity feed with timestamps and results summary
• Add date range selector for trend data
• Implement responsive layout for desktop and tablet
• Connect all components to backend API endpoints
• Add loading states, empty states, and error handling
• Write component unit tests

References

• shadcn/ui charts
• Recharts library