Function classify_pattern 

pub fn classify_pattern(
    beta_mean: &Vector2,
    beta_cov: &Matrix2,
) -> EffectPattern

Classify the effect pattern based on posterior estimates (spec §3.4.6).

An effect component is “significant” if its magnitude exceeds twice its posterior standard error: |effect| > 2×SE

Classification rules:

• UniformShift: |μ| > 2σ_μ, |τ| ≤ 2σ_τ
• TailEffect: |τ| > 2σ_τ, |μ| ≤ 2σ_μ
• Mixed: Both significant
• Indeterminate: Neither significant

Arguments

• beta_mean - Posterior mean β = (μ, τ)
• beta_cov - Posterior covariance Λ_post