netcode-revival foundation: fix cvar registry teardown SIOF + imgui RasterizerGamma

- cvar.cpp: the static FlagRegistrar destructors run during __cxa_finalize
  and touch the registry after its function-local statics are destroyed
  (static destruction-order fiasco) - the codegen tool segfaults at exit.
  Leak the registry/mutex/index so teardown order cannot bite.
- imgui_drawer.cpp: drop ImFontConfig::RasterizerGamma assignments (removed
  from imgui); keeps the build working with the modern imgui a fresh
  submodule checkout provides (the pinned imgui commit no longer exists).

src/core/cvar.cpp

@@ -34,19 +34,24 @@ std::mutex g_mutex;
 // Recursive: FlagRegistrar chain methods re-enter; change callbacks invoked
 // from SetFlagByName must not mutate the registry.
 std::recursive_mutex& GetRegistryMutex() {
-  static std::recursive_mutex m;
-  return m;
+  // Leaky (heap, never destroyed) so teardown order can't bite: static
+  // FlagRegistrar destructors run during __cxa_finalize and unregister their
+  // flags; if these function-local statics are destroyed first, that
+  // teardown crashes (static destruction-order fiasco, seen at exit of the
+  // codegen tool). Intentionally leaked - the process is ending.
+  static auto* m = new std::recursive_mutex();
+  return *m;
 }
 
 // Flag registry - use functions to avoid static init order issues
 std::vector<FlagEntry>& GetRegistryStorage() {
-  static std::vector<FlagEntry> registry;
-  return registry;
+  static auto* registry = new std::vector<FlagEntry>();
+  return *registry;
 }
 
 std::unordered_map<std::string, size_t>& GetRegistryIndex() {
-  static std::unordered_map<std::string, size_t> index;
-  return index;
+  static auto* index = new std::unordered_map<std::string, size_t>();
+  return *index;
 }
 
 std::vector<std::pair<std::string, std::string>>& GetCommandLineOverrides() {

src/ui/imgui_drawer.cpp

@@ -387,7 +387,8 @@ void ImGuiDrawer::SetupFonts() {
     // DirectWrite white-on-black edge
     // profiles (identity was measurably thinner/dimmer). The *_on_light_
     // variants below keep gamma 1.0 - dark-on-light needs no correction.
-    config.RasterizerGamma = 0.62f;
+    // (RasterizerGamma was removed from imgui's ImFontConfig; the modern
+    // rasterizer handles coverage gamma internally, so the knob is gone.)
     config.FontLoaderFlags = ImGuiFreeTypeBuilderFlags_NoHinting;
     ui_font_ = io.Fonts->AddFontFromMemoryCompressedBase85TTF(
         GetInterRegularCompressedBase85(), 18.0f, &config);
@@ -408,7 +409,7 @@ void ImGuiDrawer::SetupFonts() {
     config_on_light.RasterizerMultiply = 1.0f;
     // Dark-on-light matches the browser with NO coverage curve (harness fit:
     // identity beat every contrast/gamma variant once bake==draw size).
-    config_on_light.RasterizerGamma = 1.0f;
+    // config_on_light.RasterizerGamma = 1.0f;  (removed from imgui)
     ui_font_on_light_ = io.Fonts->AddFontFromMemoryCompressedBase85TTF(
         GetInterRegularCompressedBase85(), 18.0f, &config_on_light);
     ui_font_semibold_on_light_ = io.Fonts->AddFontFromMemoryCompressedBase85TTF(