feat(stats): collect CDN access logs and publish download statistics

Add an hourly download-stats pipeline that reads the cran-rpkgs Bunny
access logs into a download_stats schema in the build metadata database
and publishes aggregated counts to /stats/downloads.json for the
rpkgs.com /stats page.

- Classify each request (download, index, redirect reason, probe, noise)
  mirroring the edge router, and split cloud/CI networks from the rest.
- De-duplicate downloads per client, package version and day, and key
  clients on a salted HMAC so no IP is stored or published.
- Exclude our own CI runners and record run windows to show gaps.
- Declare the zone's logging settings and allow CORS for JSON.

local/missing-packages-in-index.R

@@ -39,14 +39,14 @@ files <- s3fs::s3_dir_ls(sprintf(
   "devxy-r-package-binaries-hel1/arm64/alpine320/latest/src/contrib"
 ))
 
-files_b = basename(files)
-files_b_split = sapply(strsplit(basename(files_b), "_"), function(x) x[1])
-files_b_split = setdiff(
+files_b <- basename(files)
+files_b_split <- sapply(strsplit(basename(files_b), "_"), function(x) x[1])
+files_b_split <- setdiff(
   files_b_split,
   c("PACKAGES", "PACKAGES.gz", "PACKAGES.rds", "PACKAGES.db", "Archive")
 )
 # windows-only
-files_b_split = setdiff(
+files_b_split <- setdiff(
   files_b_split,
   c(
     "PACKAGES",
@@ -67,12 +67,12 @@ files_b_split = setdiff(
     "R2wd"
   )
 )
-pkgs_index = available.packages(
+pkgs_index <- available.packages(
   "https://cran.devxy.io/amd64/jammy/latest/src/contrib"
 )[, "Package"]
-pkgs_index_b = basename(pkgs_index)
+pkgs_index_b <- basename(pkgs_index)
 if (length(files_b_split) != length(pkgs_index_b)) {
-  pkgs_missing = setdiff(files_b_split, pkgs_index_b)
+  pkgs_missing <- setdiff(files_b_split, pkgs_index_b)
   message("Packages missing in index but present in S3:")
   pkgs_missing
   formatted_pkgs <- gsub(