Build the element detail page

[ronjalh]

Goal

Compose the element detail page shown in the supplied design reference, reusing the existing components/issues instead of duplicating their responsibilities.

Suggested component structure

• ElementDetailPage: page-level data loading, composition, and loading/error/not-found states.
• ElementDetailHeader: back-to-search navigation, element code/name, and description.
• Reuse the metadata card from Create ElementMetaDataCard component #45, diagram from Create ElementDiagram component #46, actions from Create "add to gymnast"-button component #47, and variants list from Add element variants list to element page #48.
• Keep page-specific layout and data wiring in the page; keep each section focused on its own presentation and behavior.

Done when

• Load the selected element from its route/id and display its real code, name, description, difficulty, apparatus, and element group.
• Compose the header, metadata, diagram, actions, and variants in the order shown in the design reference.
• Handle loading, request errors, and an unknown element accessibly.
• Keep the layout usable on narrow and wide screens.
• Use existing CSS/Tailwind theme tokens only; do not introduce new color values.
• Use a logical heading hierarchy, meaningful image alternative text, and accessible action labels.
• Add focused tests for page states and component integration.

Related work

• Reuse component work in Create ElementMetaDataCard component #45, Create ElementDiagram component #46, Create "add to gymnast"-button component #47, and Add element variants list to element page #48; do not duplicate those issues.
• Depends on the theme utilities in Expose design tokens as Tailwind utilities #60 / PR feat: expose design tokens as Tailwind utilities #61 and the shared variant card work in PR feat: add accessible element variant card and difficulty badge #62.
• Visual reference: docs/design/elementDetail.png.