Get My Claim For Activity

Wave B (May 2026): the CLAIMANT's view of their own active claim on this activity. Used by ActivityDetail to render a calm 'Your claim status' banner so the claimant always knows where they stand — especially during 'Under ActivitIA review' (escalated_dispute / escalated_admin) when their own action is paused.

Auth: any authenticated user. Returns:

• {claim: {...}} if the current user has an active claim row, OR
• {claim: null} if they don't (200, not 404 — the FE branches on null)

Returns claim rows in ANY state (active OR terminal). If the claimant has multiple historical claims, we prefer an active one; otherwise we return the most recent terminal one so the claimant can still view the outcome from the drawer. After approve/reject/withdraw the bell notification still shows the resolved claim — the drawer mirrors that.