GUI: allow movement while open; freeze look and block bind capture

Feedback pass on the preview shell:

- Freeze the rendered view explicitly in CreateMove and again at
  FRAME_RENDER_START; CInput was still letting mouse look move the camera.
- Allow normal WASD/jump/duck movement while the GUI is open; strip
  attack/use/impulse/weapon selection so GUI clicks do not fire.
- While bind capture is active, block all game input.
- Esc no longer closes the GUI; it only cancels bind capture. F2 or the
  title-bar X close the preview.
- Interpose SDL_ShowCursor / SDL_SetRelativeMouseMode / warp / window grab so
  the game cannot re-capture or hide the native cursor while the GUI is open.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/hl2h.h b/src/hl2h.h
index 11b9014..8a81439 100644
--- a/src/hl2h.h
+++ b/src/hl2h.h
@@ -234,6 +234,7 @@ void menu_force_close();
 void gui_handle_input();
 void gui_draw();
 bool gui_is_open();
+bool gui_bind_capture_active();
 QAngle gui_frozen_view();
 // ISurface pointer (defined in menu.cpp, used for drawing tests)
 struct ISurface;