Fix Bernoulli-only sample() applied to Gaussian visible/hidden units

Matutils::sample() always binary-thresholds (src > uniform(src)), but it
was the only sampler in the codebase and was called unconditionally on
h_probs/v_probs/miniBatch in several CD Gibbs-loop branches regardless
of doGaussianVisible/doGaussianHidden. Binary-thresholding a Gaussian
unit's continuous activation is meaningless -- it would corrupt any
Gaussian-visible/hidden RBM (image-domain experiments via the GUI or
TEST target); doesn't affect poet's plain BB-RBM path since both flags
are false there.

Add sample_gaussian() (mean + N(0,1) noise) alongside the existing
Bernoulli sample() in matutils.hpp, plus Rbm::sampleVisible/sampleHidden
helpers that dispatch to the right one per the RBM's configured type.
Replace every visible/hidden Gibbs-step sample() call in cd_jens (the
active path) and cd_hinton (compiled but currently unused, behind
USE_CD_HINTON) with the appropriate dispatch helper, and fix the same
issue in Rbm::train's doSampleBatch path.

Behavior is unchanged for any RBM with doGaussianVisible/doGaussianHidden
both false (confirmed: poet.elf f output identical before/after).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016K8Gu7Qejd11JbdiHZqYAs

source/Rbm.hpp

@@ -164,7 +164,14 @@ private:
 	void cd(arma::mat const &v_states, arma::mat &dwhv, arma::mat &dbhv, arma::mat &dbv);
 	arma::mat v_to_h(const arma::mat &visible) const;
 	arma::mat h_to_v(const arma::mat &hidden) const;
-	
+
+	// Sample a visible/hidden unit's state from its probability/mean matrix,
+	// dispatching to the Bernoulli or Gaussian sampler per doGaussianVisible/
+	// doGaussianHidden -- CD's Gibbs steps must not binary-threshold a
+	// Gaussian unit's continuous activation.
+	arma::mat sampleVisible(const arma::mat &visible) const;
+	arma::mat sampleHidden(const arma::mat &hidden) const;
+
 };
 
 #endif /* RBM_HPP */