'Updated just now' is ambiguous – should reflect GitLab's last-updated time, not our last fetch

[jnwrnr]

Bug

The card footer says 'Updated ' but the timestamp is lastSyncedAt – when GitJam fetched the card, not when the work item actually changed in GitLab. On a freshly loaded board every card says 'Updated just now' regardless of whether the issue has been touched in months.

Fix

Show GitLab's updated_at field as the 'Updated' time. Keep lastSyncedAt internally for the auto-refresh freshness window (that logic is correct).

• Add updatedAt: string to CardData populated from updated_at on issue/MR/epic responses (milestones have it too).
• Card meta footer renders formatRelativeTime(card.updatedAt).
• Auto-refresh logic keeps comparing against lastSyncedAt.