fix(update): stop mcupdate asking for a GitHub username

GitHub's HTTP/2 front end began answering the anonymous git-upload-pack
POST with 401 for the git 2.39 / libcurl 7.88 build that ships with
Debian 12. Git reads any 401 as a credential request, so update.sh sat
on "Username for 'https://github.com':" against a public repo, on every
server at once, with nothing changed locally.

Pull with http.version=HTTP/1.1, which GitHub still serves anonymously,
and set GIT_TERMINAL_PROMPT=0 so a genuine auth failure errors out
instead of blocking on stdin forever. Documented in troubleshooting,
README and whatsnew, including the one-off git config for installs too
old to carry the fix.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

scripts/update.sh

@@ -40,7 +40,13 @@ echo ""
 
 # Step 1: Git pull
 info "Pulling latest changes from Git..."
-if git pull; then
+# Force HTTP/1.1 for the pull. GitHub's HTTP/2 edge rejects the anonymous
+# git-upload-pack POST sent by older git/libcurl (e.g. Debian bookworm's
+# git 2.39 + libcurl 7.88) with a 401, which git reports as a credential
+# prompt - "Username for 'https://github.com'" - even on this public repo.
+# GIT_TERMINAL_PROMPT=0 turns any auth failure into an error instead of
+# leaving the script waiting on stdin forever.
+if GIT_TERMINAL_PROMPT=0 git -c http.version=HTTP/1.1 pull; then
     success "Git pull completed"
 else
     error "Git pull failed"