Show canonical sprint IDs on every sprint card

Current, planned, and historical sprint cards should display the sprint's canonical reference (for example, sprint-2) next to the sprint title so it can be copied and used when discussing or operating on a sprint.

Acceptance criteria:

• Current, planned, and historical sprint cards show the canonical sprint reference next to the title.
• The reference uses the existing compact identifier/badge styling and remains readable at narrow card widths.
• The displayed value is the canonical sprint ref exposed by the backend, not the internal UUID.
• Existing sprint card actions, disclosure controls, and responsive layouts remain aligned.