fix(core): load the compositional models and unbreak the build tree

ROADMAP.md

@@ -6,7 +6,12 @@ occupancy work. The GitHub Wiki roadmap still needs a synchronized update; see
 
 ## Available now
 
-- `nb_glm` and `clr_welch` remain the existing differential methods.
+- The differential-abundance config offers four per-taxon count models
+  (`nb_glm`, `clr_welch`, `zinb`, `hurdle_nb`) and five compositional models
+  (`ancom_bc`, `aldex2`, `songbird`, `multinomial`, `dirichlet_multinomial`);
+  see [the differential-abundance section](README.md#differential-abundance).
+  `songbird` and `multinomial` are two implementations of the same
+  baseline-category multinomial model.
 - `zinb` and `hurdle_nb` are available in the differential-abundance config and
   UI. They report the count effect and zero/occurrence effect and test group
   effects jointly. The UI surfaces model cautions; BH adjustment remains on.

docs/statistics/zero-handling.md

@@ -105,6 +105,10 @@ there is no silent fallback to another estimator.
   valid observations under that model.
 - Raise `min_prevalence` when rare taxa would make imputed values dominate the
   composition. The result reports median and maximum imputed mass per sample.
+- Use `multinomial` or `dirichlet_multinomial` when the whole composition is the
+  unit of inference: a zero count is part of the likelihood, no size factor is
+  fitted, and conditioning on each sample's read total makes every effect a log
+  ratio against a reference taxon rather than an absolute abundance.
 - Consider an occupancy/observation model when detection itself is the object of
   inference, or a zero-inflated or hurdle model when structural and sampling
   zeros must be separated. Those models are not implemented by `clr_welch`, and