tulpa 0.0.198

• tulpa_re_aghq() returns the mode/theta cross-Hessian block (#398).
  Adds blup_cross (Bf) to the return value: the per-group -d^2 ell_g / d theta db block at the mode, needed to draw a group's BLUP jointly with
  theta instead of independently (Cinv %*% t(Bf) is the first-order
  db_hat/dtheta correction) -- the same joint-draw contract
  .tobs_community_em()-based tulpaObs families already expose via their own
  Cinv/Bf. Computed via a cheap central finite difference of
  theta_score over b (O(d) oracle calls, independent of n_theta).
  Declines to NA (never a silent 0) when the oracle's theta_score has no
  analytic implementation, as on the R-closure bridge (make_site/
  make_group) -- REGroupOracle gains has_theta_score() to signal this.
  Verified against the closed-form binomial-GLMM cross term and an
  independent finite-difference re-solve of the group's mode under a
  perturbed theta. Unblocks gcol33/tulpaObs#220 (ms_abun()'s posterior-SBC
  registration).

• tulpa_re_aghq() also returns the FULL per-group joint covariance
  across RE terms (blup_cov_g, blup_cross_g). blup_var only ever
  exposed the per-term diagonal of a group's posterior covariance; when a
  group carries more than one RE term sharing the same grouping factor (e.g.
  an abundance-arm term and a detection-arm term on the same species), the
  group's mode is found jointly across every term's coefficients, so real
  posterior covariance can exist BETWEEN terms -- cpp_aghq_blups() already
  inverts the full joint Hessian to get it, it just discarded everything off
  the diagonal before this. Drawing a group's terms independently would
  repeat gcol33/tulpaObs#226 one level deeper (inside a group instead of
  between theta and a group). Validated against a closed-form joint-Hessian
  construction on a toy model with deliberately collinear RE terms; the new
  diagonal is byte-identical to the pre-existing blup_var.