feat(menu): submenú "Jugabilitat" al menú de servei amb tres toggles

Nou apartat al ServiceMenu (entre Controls i Sistema) amb tres toggles
ON/OFF connectats a GameplayConfig: látec travessa sarcs, foc amic,
col·lisió entre jugadors. Cada canvi crida save() immediatament, així
l'estat persisteix entre sessions sense necessitat de "aplicar".

Locales ca/en: claus `tweaks` + tres `menu.items.*` corresponents.

source/game/ui/service_menu.cpp

@@ -17,6 +17,7 @@
 #include "core/rendering/text.hpp"
 #include "core/system/event_buffer.hpp"
 #include "core/ui/ui_config.hpp"
+#include "game/gameplay_config.hpp"
 #include "game/options.hpp"
 #include "game/options_apply.hpp"
 #include "utils/defaults.hpp"
@@ -692,6 +693,8 @@ auto ServiceMenu::buildRoot() -> Page {
         []() { ServiceMenu::get().pushPage(buildAudio()); }));
     page.items.push_back(makeSubmenu("menu.items.controls_submenu",
         []() { ServiceMenu::get().pushPage(buildControls()); }));
+    page.items.push_back(makeSubmenu("menu.items.tweaks_submenu",
+        []() { ServiceMenu::get().pushPage(buildTweaks()); }));
     page.items.push_back(makeSubmenu("menu.items.system_submenu",
         []() { ServiceMenu::get().pushPage(buildSystem()); }));
     return page;
@@ -1155,6 +1158,42 @@ void ServiceMenu::startDefineButtons(SDL_Gamepad* pad, const std::string& name,
     define_buttons_.enable(pad, name, path);
 }
 
+auto ServiceMenu::buildTweaks() -> Page {
+    // Submenú "Tweaks" — flags de jugabilitat persistits a `gameplay.yaml`
+    // dins la carpeta de sistema. Cada toggle muta `GameplayConfig` i
+    // n'invoca `save()` immediatament: l'usuari veu el canvi reflectit al
+    // joc sense esperar a un "aplicar" i, si tanca el joc, torna en el
+    // mateix estat. Tres toggles ON/OFF, sense estat addicional.
+    Page page;
+    page.title_key = "menu.titles.tweaks";
+
+    page.items.push_back(makeToggle(
+        "menu.items.whip_pierces_walls",
+        []() { return GameplayConfig::get().whipDamagePiercesWalls(); },
+        [](bool v) {
+            GameplayConfig::get().setWhipDamagePiercesWalls(v);
+            GameplayConfig::get().save();
+        }));
+
+    page.items.push_back(makeToggle(
+        "menu.items.friendly_fire",
+        []() { return GameplayConfig::get().friendlyFire(); },
+        [](bool v) {
+            GameplayConfig::get().setFriendlyFire(v);
+            GameplayConfig::get().save();
+        }));
+
+    page.items.push_back(makeToggle(
+        "menu.items.players_collide",
+        []() { return GameplayConfig::get().playersCollide(); },
+        [](bool v) {
+            GameplayConfig::get().setPlayersCollide(v);
+            GameplayConfig::get().save();
+        }));
+
+    return page;
+}
+
 auto ServiceMenu::buildSystem() -> Page {
     Page page;
     page.title_key = "menu.titles.system";