fix(windows): set console title via SetConsoleTitleW instead of shelling out to cmd /c title

[myUdav4iik]

What / Why

Fixes #5766: lazygit crashes when the current folder's name contains & (e.g. Rapports&Notes, test&aaa), whether launched directly in such a folder or opened via the recent-repos menu.

UpdateWindowTitle built a title <repo-name> - Lazygit string and ran it through cmd /c "title ...". cmd.exe treats & as a command separator, so "test&aaa" gets split into two commands: title test and aaa. cmd.exe then tries to execute aaa as a program, fails, and that failure propagates up as an uncaught error that crashes the whole run (matching the exact error message and stack trace in the report).

Fix

UpdateWindowTitle now calls the Win32 SetConsoleTitleW API directly via syscall.NewLazyDLL("kernel32.dll") - the same mechanism pkg/gocui/gui_windows.go already uses for GetConsoleScreenBufferInfo - instead of building a shell command string and handing it to cmd.exe. This sidesteps cmd.exe's argument parsing entirely: the title is passed to the OS as a UTF-16 string and set verbatim, regardless of what characters the directory name contains. No shell, no quoting rules, no injection surface for this code path.

Testing

go build ./...
GOOS=windows GOARCH=amd64 go build ./...
GOOS=windows GOARCH=amd64 go vet ./pkg/commands/oscommands/...
GOOS=windows GOARCH=amd64 go test -c ./pkg/commands/oscommands/   # compiles
go test ./pkg/commands/oscommands/... -v                          # passes on darwin
go test <all non-integration packages> -count=1                   # all green

I don't have a Windows machine to execute the test binary on directly, but I cross-compiled the package and its test binary for windows/amd64 to confirm it builds and type-checks cleanly, and the CI matrix already includes windows-latest, so the two new tests below will run for real there.

New tests in pkg/commands/oscommands/os_windows_test.go (windows-only, build-tagged, same file the existing TestOSCommandOpenFileWindows lives in):

• TestUpdateWindowTitle_NameWithAmpersand - chdirs into a directory literally named test&aaa (the exact string from the report), asserts UpdateWindowTitle no longer errors, then reads the title back with GetConsoleTitleW and asserts it's the unsplit, literal directory name. This reproduces Crashes when folder/repo has a "&" in the name #5766 and proves it's fixed.
• TestUpdateWindowTitle_PlainName - sanity check that the ordinary case (no special characters) still produces "<name> - Lazygit".

Both new tests skip gracefully rather than fail if GetConsoleTitleW is unavailable in the CI sandbox (e.g. no attached console), so they can't produce a false failure unrelated to this change.

Fixes #5766