fix: create dists/error codename alias and fix cp -r overwrite bug

dists/error was never written to gh-pages because the codename alias
code was added after the v3.2.0 tag. The stable publish job only runs
on v*.*.* tags, so all subsequent pushes to release/3.x only touched
dists/testing. Bumping to v3.2.1 triggers stable publish to create it.

Also fix: cp -r src dst when dst already exists puts src inside dst
rather than replacing it. Add rm -rf before cp -r to guarantee a clean
replace on every stable release.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/build.yml

@@ -450,9 +450,11 @@ jobs:
 
           # Create codename alias directories (e.g. dists/error/ mirrors dists/v3/)
           # so that both Suite ("v3") and Codename ("error") work in sources.list.
+          # rm -rf first: cp -r puts src inside dst when dst already exists.
           for DIST in $DISTS; do
             CODENAME=$(_dist_codename "$DIST")
             if [[ "$CODENAME" != "$DIST" ]]; then
+              rm -rf "${PAGES_DIR}/dists/${CODENAME}"
               cp -r "${PAGES_DIR}/dists/${DIST}" "${PAGES_DIR}/dists/${CODENAME}"
             fi
           done