Move sprint issue disclosure to the card footer and label its state

Problem

Planned and historical sprint cards place an icon-only issue disclosure control at the top left. The location competes with the sprint heading, and the icon does not clearly communicate whether it will show or hide the sprint's issues.

Collapsed sprint cards also develop unstable alignment when the card or viewport becomes narrow. Metadata and action buttons wrap or shift unpredictably, with header actions sometimes dropping to the bottom of the card. This makes otherwise identical cards look structurally different depending on available width.

Desired behavior

Treat issue membership as a secondary card action: place the disclosure at the bottom right and pair its icon with explicit state text. Keep sprint identity, schedule/status metadata, and header actions aligned through intentional responsive layouts rather than allowing individual controls to fall into arbitrary positions.

Acceptance criteria

• Move the issue disclosure control to the bottom-right footer area of planned sprint cards.
• Apply the same placement to completed sprint-history cards.
• Label the collapsed action Show issues and the expanded action Hide issues.
• Keep the icon and update aria-expanded, the accessible name, and visible text together when state changes.
• Preserve stable alignment for sprint metadata and header actions when collapsed cards become narrow.
• Use an intentional responsive reflow for metadata/actions; header controls must not unexpectedly drop into the card footer or change order.
• Keep the issue disclosure as the only action intentionally anchored in the bottom-right footer area.
• Handle long sprint names and normal schedule/completion metadata without overlapping controls or producing uneven card structure.
• Preserve the current lazy-loading, pagination, and show/hide behavior for issue membership.
• Keep issue disclosure independent from the sprint description's See more expansion.
• Ensure both collapsed and expanded layouts work on narrow screens and match existing button, focus, hover, and dark-mode patterns.
• Add render/integration coverage for planned and historical cards at wide and narrow widths, with collapsed and expanded issue states.