feat(scenes): afegir placeholders LogoScene/TitleScene/IntroScene

Tres escenes de 5 s cadascuna, activables al flux que precedeix GameScene.
Classes separades (sense base comuna) perquè divergiran quan es
desenvolupi contingut real.

Avancen per timeout o per qualsevol tecla no reservada. Les tecles
reservades (F1-F12, Escape) són les declarades a data/input/keys.yaml i
mantenen el seu comportament habitual via GlobalInputs. La
classificació viu a Placeholder::isReservedScancode, i KeyConfig exposa
bindings() per enumerar-les sense duplicar la llista.

Encara no integrats al Director: això es fa al següent commit quan
s'afegeix el selector d'escena inicial.

source/game/scenes/title_scene.cpp

@@ -0,0 +1,85 @@
+#include "game/scenes/title_scene.hpp"
+
+#include <SDL3/SDL.h>
+
+#include <algorithm>
+#include <cstdint>
+#include <iostream>
+#include <string>
+#include <utility>
+
+#include "core/input/global_inputs.hpp"
+#include "core/rendering/notifier.hpp"
+#include "core/rendering/render_info.hpp"
+#include "core/rendering/screen.hpp"
+#include "core/rendering/text.hpp"
+#include "core/system/event_buffer.hpp"
+#include "game/options.hpp"
+#include "game/scenes/placeholder_input.hpp"
+#include "game/ui/ui_palette.hpp"
+#include "utils/defaults.hpp"
+#include "utils/defines.hpp"
+
+namespace {
+
+    constexpr int NAME_Y_OFFSET = -8;
+    constexpr int TIMER_Y_OFFSET = 8;
+    // TODO: migrar a un logger unificat quan es decideixi (veure INC-03 a
+    // docs/audit-core-rendering.md).
+    const char* const SCENE_NAME = "TITLE";
+
+}  // namespace
+
+TitleScene::TitleScene(std::shared_ptr<Text> font, SceneFactory next_factory)
+    : font_(std::move(font)),
+      next_factory_(std::move(next_factory)) {
+    std::cout << "[scene] " << SCENE_NAME << " start\n";
+}
+
+TitleScene::~TitleScene() = default;
+
+void TitleScene::update(int delta_ms) {
+    GlobalInputs::update(delta_ms);
+    if (GlobalInputs::wantsQuit()) {
+        wants_quit_ = true;
+        return;
+    }
+
+    timer_ms_ -= delta_ms;
+
+    const bool SKIPPED = std::ranges::any_of(EventBuffer::events, [](const SDL_Event& ev) {
+        return ev.type == SDL_EVENT_KEY_DOWN && !Placeholder::isReservedScancode(ev.key.scancode);
+    });
+
+    if ((timer_ms_ <= 0 || SKIPPED) && next_factory_) {
+        next_scene_ = next_factory_();
+    }
+
+    Notifier::get().update(delta_ms);
+    RenderInfo::get().update(delta_ms, Options::buildRenderInfoFrame(UiColor::RENDER_INFO_TEXT, UiColor::RENDER_INFO_SHADOW));
+}
+
+void TitleScene::render() {
+    constexpr std::uint32_t BLACK_ARGB = 0xFF000000U;
+    Screen::get().fillRect(0, 0, GameCanvas::WIDTH, GameCanvas::HEIGHT, BLACK_ARGB);
+
+    if (font_) {
+        const int SECS_LEFT = std::max(1, (timer_ms_ + 999) / 1000);
+        font_->writeDX(Text::CENTER_FLAG | Text::COLOR_FLAG,
+            GameCanvas::CENTER_X,
+            GameCanvas::CENTER_Y + NAME_Y_OFFSET,
+            SCENE_NAME,
+            1,
+            Defaults::UI::NOTIFICATION_TEXT);
+        font_->writeDX(Text::CENTER_FLAG | Text::COLOR_FLAG,
+            GameCanvas::CENTER_X,
+            GameCanvas::CENTER_Y + TIMER_Y_OFFSET,
+            std::to_string(SECS_LEFT),
+            1,
+            Defaults::UI::NOTIFICATION_TEXT);
+    }
+
+    Notifier::get().render();
+    RenderInfo::get().render();
+    Screen::get().present();
+}