2.7.1-Windows

Performance enhancements: optimize runtime footprint and fix autoclose race condition (v2.7.1)

• Fix data race on autoclose flag: replaced unguarded global bool with
  atomic.Bool field on App struct, eliminating concurrent read/write
  between the monitoring goroutine and AutoClose()
• Cache exe directory via sync.Once (getExeDir): removed repeated
  os.Executable() syscalls from getCacheDir, setupLogging, ReadLogFile
  and NewApp — most notably from the asset server hot path, which was
  called on every image request from the WebView2 gallery
• Cache GetAppInfo result via sync.Once: wails.json is embedded at
  compile time and never changes; json.Unmarshal now runs only once
• Cache isAdmin result via sync.Once and promote IsUserAnAdmin to a
  package-level proc var, consistent with all other Win32 proc declarations
• Eliminate redundant file open in processAndResizeImage: image is now
  opened once; io.Seek(0, SeekStart) rewinds the reader when a full
  decode is needed, removing a second syscall on every image cache write