Show ticket completion rate over time on the project About page

Goal

Add a compact graph to the project About page showing how ticket completion changes over time.

Acceptance criteria

• The About page displays a time-series graph of ticket completion rate for the current project.
• Define the metric and denominator clearly in the UI, including how reopened, deleted, and newly created tickets affect historical values.
• Use project-local ticket history rather than reconstructing past rates from only the current issue state.
• Provide sensible date buckets and a useful default range, with readable empty and insufficient-data states.
• Include an accessible text/table summary or equivalent for users who cannot consume the visual graph.
• The graph is responsive and matches existing light/dark UI patterns.
• Read-only and public viewers can see the graph when they can view the About page; no inaccessible project data is included.
• Add metric, authorization, rendering, and boundary-date coverage.