GUI: add F2 preview shell with dummy controls

First vertical slice for the custom ISurface GUI:

- window/sidebar/content shell with Movement, Combat, Visuals, Weapons and
  System categories;
- cards with dummy Active/Bind, collapsible settings, toggles, sliders,
  buttons, bind capture, scrolling and tooltips;
- native OS cursor by releasing SDL relative mode; reasserted while open;
- F2 toggles the preview; Insert still opens the old text tree;
- while the GUI is open, do_move freezes movement/buttons/impulses/view and
  skips combat features; ESP and the speed graph keep drawing.

Dummy controls do not touch the real config yet. The text menu is removed
after feature parity in the next pass.

1 files changed, 19 insertions, 0 deletions

diff --git a/src/hl2h.cpp b/src/hl2h.cpp
index c4f8aad..c0c27af 100644
--- a/src/hl2h.cpp
+++ b/src/hl2h.cpp
@@ -540,6 +540,25 @@ static void do_move(int seq, float frametime) {
   bool inwater = (flags & FL_INWATER) != 0;
   const float *vel = (const float *)(e + g_net.velocity);
 
+  if (gui_is_open()) {
+    QAngle f = gui_frozen_view();
+    g_cam_view = Vector{f.x, f.y, f.z};
+    cmd->viewangles[0] = f.x;
+    cmd->viewangles[1] = f.y;
+    cmd->viewangles[2] = f.z;
+    cmd->forwardmove = 0.0f;
+    cmd->sidemove = 0.0f;
+    cmd->upmove = 0.0f;
+    cmd->buttons = 0;
+    cmd->impulse = 0;
+    cmd->weaponselect = 0;
+    cmd->weaponsubtype = 0;
+    cmd->mousedx = 0;
+    cmd->mousedy = 0;
+    note_modified(cmd, flags, vel);
+    return;
+  }
+
   bool bhop_on = feature_active(FEAT_BHOP);
   bool abh_on = feature_active(FEAT_ABH);