Show canonical sprint refs beside sprint titles

Problem

Current, planned, and historical sprint views show the sprint title but not its canonical public identifier. This makes it unnecessarily difficult to reference a sprint in conversation, documentation, URLs, API/MCP operations, or support requests.

Desired behavior

Show the stable public sprint ref, such as sprint-2, next to the sprint title everywhere a sprint is presented as a primary card or page heading. Do not expose the internal database UUID.

Acceptance criteria

• Show the canonical sprint ref beside the title of the active/current sprint.
• Show the canonical sprint ref beside titles on planned sprint cards.
• Show the canonical sprint ref beside titles on completed sprint-history cards and the historical sprint detail/issue view.
• Use one consistent compact badge/text treatment across all three sprint states.
• Keep the ref readable, selectable, and visually secondary to the human sprint title.
• Do not substitute the sprint's internal UUID or its position in the current list.
• Preserve alignment for long sprint titles and narrow cards without crowding metadata or action controls.
• Match existing responsive, light/dark, and accessibility patterns.
• Add render/integration tests proving the correct ref appears for current, planned, and historical sprints.