ci(repo-stats): swap actions/checkout for direct git clone on gh-pages

    The PAT-token swap didn't fix the gh-pages fetch — same opaque "exit
    code 1" from actions/checkout@v4 on both attempts of the retry loop,
    with no underlying git stderr surfaced. Likely the wildcard-refspec
    + shallow fetch pattern v4 uses combined with something at the runner
    side, but the action's swallowed errors make it untriagable from logs.

    Replacing the gh-pages checkout with `git clone --branch gh-pages
    --depth 1` using the same PAT, embedded in the URL. Direct, explicit,
    and if anything goes wrong the real git error reaches the log instead
    of "exit code 1". The recorded remote keeps the PAT, so the later
    `git push` reuses it — no separate auth setup needed.

    Identity config (user.name / user.email) moved into the clone step so
    it lives on the freshly cloned repo; dropped the now-duplicate config
    calls from commit-and-push.

    Source checkout still uses actions/checkout@v4 since it never had a
    problem (the default ref is the workflow's own commit, no wildcard
    refspec required).