Fix compliance dashboard chart visualisation

[Brook4747]

Summary

This PR has fixed the custom chart visualization feature of the dashboard.
Users can now select different chart types when viewing compliance results. Previously, due to an error, the charts were not visible and the available chart types were:

• Pie chart
• Doughnut chart
• Bar chart

Type of Change

• Added chart type selector dropdown
• Added chart type state management
• Updated ComplianceChart to support multiple chart types
• Added fallback handling for empty datasets
• Maintained dark mode compatibility

Affected Components

• /backend-api
• /frontend
• /engine (collectors / policies)
• /security
• /infrastructure
• /.github/workflows
• /docs

Motivation

Testing

Manually tested:

• Dashboard loads successfully
• Pie Chart renders correctly
• Doughnut Chart renders correctly
• Bar Chart renders correctly
• Chart switching works without page crashes
• Dark mode display remains functional

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[chatgpt-codex-connector]

Treat zero-total pie data as no data

When the selected scan has no results yet (for example, a first-run dashboard, a pending/running scan, or a scan whose counts are all zero), Dashboard still passes labels=["Pass", "Fail"] and values=[0, 0], so this length-only fallback is skipped. The pie/doughnut chart is then asked to render an all-zero series instead of the intended No data state, leaving empty dashboards with a blank or invalid chart rather than the fallback this component is trying to provide.

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