refactor: introduir Config::EngineConfig com a struct POD a core/

Pas 1/N del hallazgo #28. Sense canvi de comportament:

Nou: source/core/config/engine_config.hpp
- Defineix Config::EngineConfig (POD) amb les sub-structs WindowConfig,
  RenderingConfig, KeyboardBindings, GamepadBindings, PlayerBindings i
  el flag console.
- Sense singletons ni virtuals; la inversió real es fa en commits
  posteriors injectant Config::EngineConfig& per constructor.

Modificat: source/game/options.hpp
- Elimina les struct definitions locals (Window, Rendering, ...).
- Afegeix Options::engine_config (única font de veritat).
- Conserva Options::window, Options::rendering, player1, player2,
  keyboard_controls, gamepad_controls i console com a referències
  inline a camps d'engine_config. Cost runtime zero, callsites
  existents no requereixen cap canvi.

Hallazgo #28 de CODE_REVIEW.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

source/core/config/engine_config.hpp

@@ -0,0 +1,61 @@
+// engine_config.hpp - Configuració runtime del motor (window, render, input)
+// © 2026 JailDesigner
+//
+// Struct POD que conté la configuració runtime que els sistemes de `core/`
+// llegeixen i muten. La capa de persistència (YAML) viu a `game/options.cpp`,
+// que omple aquesta struct a init() i loadFromFile().
+//
+// Es passa per referència (mutable quan cal) al constructor dels sistemes
+// que la necessiten, mantenint `core/` agnòstic a `game/`.
+
+#pragma once
+
+#include <SDL3/SDL.h>
+
+#include <string>
+
+namespace Config {
+
+    struct WindowConfig {
+        int width{1280};
+        int height{720};
+        bool fullscreen{false};
+        float zoom_factor{1.0F};  // Zoom level (0.5x to max_zoom)
+    };
+
+    struct RenderingConfig {
+        int vsync{1};  // 0=disabled, 1=enabled
+    };
+
+    struct KeyboardBindings {
+        SDL_Scancode key_left{SDL_SCANCODE_LEFT};
+        SDL_Scancode key_right{SDL_SCANCODE_RIGHT};
+        SDL_Scancode key_thrust{SDL_SCANCODE_UP};
+        SDL_Scancode key_shoot{SDL_SCANCODE_SPACE};
+        SDL_Scancode key_start{SDL_SCANCODE_1};
+    };
+
+    struct GamepadBindings {
+        int button_left{SDL_GAMEPAD_BUTTON_DPAD_LEFT};
+        int button_right{SDL_GAMEPAD_BUTTON_DPAD_RIGHT};
+        int button_thrust{SDL_GAMEPAD_BUTTON_WEST};  // X button
+        int button_shoot{SDL_GAMEPAD_BUTTON_SOUTH};  // A button
+    };
+
+    struct PlayerBindings {
+        KeyboardBindings keyboard{};
+        GamepadBindings gamepad{};
+        std::string gamepad_name;  // Empty = auto-assign by index
+    };
+
+    struct EngineConfig {
+        WindowConfig window{};
+        RenderingConfig rendering{};
+        PlayerBindings player1{};
+        PlayerBindings player2{};
+        KeyboardBindings keyboard_controls{};  // Defaults globals per Input
+        GamepadBindings gamepad_controls{};
+        bool console{false};
+    };
+
+}  // namespace Config