Fix window geometry save/restore: DPI scaling, position drift, maximized state

- LFM: Position = poDesigned (was poScreenCenter, overriding our restore)
- RestoreWindowBounds: remove position scaling (L,T invariant across DPI);
  scale size correctly per backend: LCLWin32 uses CurDPI/SavedDPI (physical px),
  Qt6/GTK/Cocoa use SavedDPI/CurDPI (logical px, inverse); fix min-size
  inflation on Qt6 (was MulDiv(900,DPI,96) which exceeds logical screen width
  at 150%+ scale, forcing window to 0,0)
- SaveWindowBounds moved from FormDestroy to FormClose while window is still
  stable; add guard for bogus RestoredLeft/Top values on Qt6 when maximized
- RestoreWindowBounds stores FRestoreL/T and re-applies position in AfterShowTick
  (200ms after show) when WM frame extents are already known to Qt, fixing the
  systematic right/down drift caused by unknown frame extents at FormCreate time
- Save and restore WindowState (maximized flag); skip AfterShowTick position
  re-apply when window is maximized

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

MainForm.lfm

@@ -8,7 +8,7 @@ object MainForm: TMainForm
   Font.Color = clSilver
   Font.Height = -13
   Font.Name = 'Courier New'
-  Position = poScreenCenter
+  Position = poDesigned
   LCLVersion = '4.6.0.0'
   OnClose = FormClose
   OnCreate = FormCreate