Return clear error on user delete FK violation

Deleting a membership profile referenced by other tables (owner,
approver, assignee, etc.) surfaced as a generic Internal error.
Detect the Postgres FK violation (23503) in the coredata Delete,
return ErrResourceInUse, and map it to CONFLICT in the GraphQL
and MCP resolvers so the client sees an actionable error.

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/coredata/membership_profile.go

@@ -1416,6 +1416,11 @@ WHERE
 
 	_, err := conn.Exec(ctx, q, args)
 	if err != nil {
+		if pgErr, ok := errors.AsType[*pgconn.PgError](err); ok {
+			if pgErr.Code == "23503" {
+				return ErrResourceInUse
+			}
+		}
 		return fmt.Errorf("cannot delete profile: %w", err)
 	}