fix: restore correct remote URL in git snapshots

[nssherpa]

When generating a snapshot, git clone <local-mirror-path> causes Git to write the local mirror path as remote.origin.url in the snapshot's .git/config. After clients extract the snapshot and run git pull, Git tries to reach the local path (e.g. /app/state/git-mirrors/github.com/squareup/java) which doesn't exist on their machine.

Fix: after the local clone, run git remote set-url origin <upstream> to restore the correct upstream URL before archiving the snapshot.

Testing

1. Start cachew

just docker build && docker run --rm -it \
  -p 8080:8080 \
  -v ~/.scripts/github/blox-cache.2026-02-03.private-key.pem:/app/github-app-key.pem:ro \
  -e CACHEW_GITHUB_APP_APP_ID="2666596" \
  -e CACHEW_GITHUB_APP_PRIVATE_KEY_PATH="/app/github-app-key.pem" \
  cachew:local

2. Clone a repo

time git clone --depth 1000 http://localhost:8080/git/github.com/block/cachew.git ~/Development/gitclones/cachew-clone

3. Fetch snapshot

time sh -c 'mkdir ~/Development/gitclones/cachew-stream &&  curl http://localhost:8080/git/github.com/block/cachew.git/snapshot.tar.zst | zstd -dc | tar -xpf - -C ~/Development/gitclones/cachew-stream'

4. cd into the tar-d repo and run git pull, check git config, etc. The url is now correct.

cd ~/Development/gitclones/cachew-stream
Hermit environment /Users/nsherpa/Development/gitclones/cachew-clone deactivated
Hermit environment /Users/nsherpa/Development/gitclones/cachew-stream activated
❯ git pull --rebase
Already up to date.
❯ cat .git/config
[core]
	repositoryformatversion = 0
	filemode = true
	bare = false
	logallrefupdates = true
[remote "origin"]
	url = http://127.0.0.1:8080/git/github.com/block/cachew
	fetch = +refs/heads/*:refs/remotes/origin/*
[branch "main"]
	remote = origin
	merge = refs/heads/main

previously it would be something like this

🐚 bloxer@workstation-25886-7f94ff4c9c-4jkw8:~/java-stream$ cat .git/config 
[core]
        repositoryformatversion = 0
        filemode = true
        bare = false
        logallrefupdates = true
[remote "origin"]
        url = /app/state/git-mirrors/github.com/squareup/java
        fetch = +refs/heads/*:refs/remotes/origin/*
[branch "master"]
        remote = origin
        merge = refs/heads/master