fix: percent escaping for git --format on Windows (#629)

* test(server): add real-spawn round-trip for % in argv

RED test: pass --format=%(refname)... through spawnProcess to a child
node script that echoes argv[2]. Asserts the child receives the original
string verbatim. Wired into the Windows CI matrix to expose the
escapeWindowsCmdValue %-doubling bug under cmd.exe.

* test(server): use bare 'node' command so cmd.exe path is exercised

process.execPath has both an extension and a path separator on Windows,
so shouldUseWindowsShell returns false and the broken %-escape pipeline
is never invoked. Use the bare command name 'node' instead.

* fix(server): stop doubling % in cmd.exe arg escaping on Windows

cmd.exe only collapses `%%` → `%` inside batch files; on the command
line / via `cmd /c "..."` `%%` stays literal. Doubling `%` in
escapeWindowsCmdValue meant args like `--format=%(refname)` reached git
as `--format=%%(refname)`, which git interprets as the escape sequence
for a literal `%`, so format atoms appeared verbatim and the branch
picker showed `%(refname)%09%(committerdate:unix)` instead of branch
names.

Update unit tests that pinned the broken doubling behavior.

packages/server/src/utils/windows-command.ts

@@ -10,7 +10,11 @@ function escapeWindowsCmdValue(value: string): string {
 
   const isQuoted = value.startsWith('"') && value.endsWith('"');
   const unquoted = isQuoted ? value.slice(1, -1) : value;
-  const escaped = unquoted.replace(/%/g, "%%").replace(/([&|^<>()!])/g, "^$1");
+  // Do NOT double `%` here. cmd.exe only collapses `%%` → `%` inside batch
+  // files; on the command line / `cmd /c "..."` `%%` stays literal, which
+  // breaks args like git's `--format=%(refname)` (git treats `%%` as the
+  // escape for a literal `%`, so the format atoms become literals).
+  const escaped = unquoted.replace(/([&|^<>()!])/g, "^$1");
 
   if (isQuoted || /[\s"]/u.test(unquoted)) {
     const quoted = escaped