ci: replace Jenkins with Gitea Actions, modernize DESCRIPTION

- Add real R CMD check workflow via Gitea Actions (rocker/r-ver:4.4)
- Remove Jenkinsfile and demo workflow
- Modernize DESCRIPTION: Authors@R, R >= 4.1.0, URL/BugReports fields,
  move tidycensus from Imports to Suggests, testthat edition 3
- Fix agresti_coull_interval: correct implementation, export it
- Convert get_fips/get_stabbr to use requireNamespace for tidycensus
- Remove civilytics:: self-reference in rnh()

R/prop_conf.R

@@ -72,14 +72,21 @@ waldInterval <- function(x, n, conf.level = 0.95){
 
 #' Calculate the Agresti-Coull interval
 #'
-#' @param num a number of successes
-#' @param den a number of trials
-#' @param conf.level default 0.95, set the confidence interval to return
+#' @param num number of successes
+#' @param den number of trials
+#' @param conf.level default 0.95, confidence level for the interval
 #'
-#' @return an interval
-agresti_coull_interval <- function(num, den, conf.level) {
-  num <- num + 2
-  den <- den + 4
-  return(num/den)
-
+#' @return three values forming the lower bound, observed proportion, and upper bound
+#' @export
+#'
+#' @examples
+#' agresti_coull_interval(20, 40)
+#' agresti_coull_interval(2, 100, conf.level = 0.99)
+agresti_coull_interval <- function(num, den, conf.level = 0.95) {
+  z <- qnorm(1 - (1 - conf.level) / 2)
+  n_tilde <- den + z^2
+  p_tilde <- (num + z^2 / 2) / n_tilde
+  margin <- z * sqrt(p_tilde * (1 - p_tilde) / n_tilde)
+  obs <- num / den
+  return(c("low" = p_tilde - margin, "observed" = obs, "high" = p_tilde + margin))
 }