Name the master branch explicitly when cloning and pulling

A bare `git clone` follows whatever the remote advertises as its default
branch. Pushing --all to a fresh Gitea repo left that default pointing at
autobuyer, so setup cloned a branch predating the build fixes and failed at
`next build` on an error that had already been fixed on master.

The Gitea default is corrected, but the script no longer depends on it:
clone passes --branch master, and the update path fetches, checks out master
and pulls it by name. That also recovers a checkout already stranded on the
wrong branch, rather than needing the folder deleted.

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

setup-windows.bat

@@ -180,24 +180,39 @@ echo  Installing to: %TARGET%
 echo.
 
 REM -------------------------------------------------------------- clone / pull
-if exist "%TARGET%\.git" (
-    echo  [1/5] Existing checkout found - pulling latest...
-    pushd "%TARGET%"
-    git pull --ff-only
-    if errorlevel 1 (
-        popd
-        echo  [X] git pull failed. Resolve local changes and re-run.
-        goto :fail
-    )
-    popd
-) else (
-    echo  [1/5] Cloning %REPO_URL% ...
-    git clone "%REPO_URL%" "%TARGET%"
-    if errorlevel 1 (
-        echo  [X] Clone failed. Check network access to git.juicerroom.com.
-        goto :fail
-    )
-)
+REM The branch is named explicitly throughout. A bare `git clone` follows the
+REM remote's default branch, which is not necessarily master - and an existing
+REM checkout may be sitting on a stale branch from before that was corrected.
+if exist "%TARGET%\.git" goto :repo_update
+echo  [1/5] Cloning %REPO_URL% ...
+git clone --branch master "%REPO_URL%" "%TARGET%"
+if errorlevel 1 goto :clone_failed
+goto :repo_ready
+
+:clone_failed
+echo  [X] Clone failed. Check network access to git.juicerroom.com.
+goto :fail
+
+:repo_update
+echo  [1/5] Existing checkout found - switching to master and pulling...
+pushd "%TARGET%"
+git fetch origin
+if errorlevel 1 goto :pull_failed
+git checkout master
+if errorlevel 1 goto :pull_failed
+git pull --ff-only origin master
+if errorlevel 1 goto :pull_failed
+popd
+goto :repo_ready
+
+:pull_failed
+popd
+echo  [X] Could not update the checkout. If you have local changes, either
+echo      commit them or delete this folder and re-run to clone fresh:
+echo        %TARGET%
+goto :fail
+
+:repo_ready
 
 pushd "%TARGET%"