Fixed bootstrap confidence interval computation. The previous version
used stats::update() to refit models on bootstrap samples, which
failed silently when bootstrap data frames had duplicate row names
produced by sampling with replacement. All confidence intervals were
returning NA. The fix replaces stats::update() with direct
stats::glm() calls and resets row names on each bootstrap sample.
All bootstrap replicates now succeed and confidence intervals are
correctly computed.
Fixed balance SMD computation: max_smd and n_above now handle
edge cases with near-constant covariates without returning NA.
Added n_boot_valid diagnostic field to fit$effects reporting the
number of successful bootstrap replicates.
Improved warning messages when bootstrap replicates fail.
Removed pkgdown URL from DESCRIPTION (was returning 404). Only the GitHub repository URL is now listed.