Move main menu start-game cutscene from ui panel to scene

The load-all-slots/no-device cutscene and its helper callbacks belong to
scene-level game flow, not the uimainmenu UI panel. Moved them into
scenemainmenu.c/h behind a new sceneMainMenuStartGame() entry point;
uimainmenu.c's Start Game handler now just calls that.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/dusk/scene/mainmenu/scenemainmenu.c

@@ -7,6 +7,73 @@
 
 #include "scenemainmenu.h"
 #include "ui/screen/mainmenu/uimainmenu.h"
+#include "ui/dialog/save/uiselectsave.h"
+#include "rpg/cutscene/cutscene.h"
+#include "rpg/cutscene/cutscenesystem.h"
+#include "scene/scene.h"
+
+void sceneMainMenuOpenSelectSave(void *userData);
+
+// Loads every save slot before opening the load-game picker, same
+// checking/retry-on-error shape as the initial scene's device lookup
+// (see scene/initial/sceneinitial.c) - the error branch loops back via
+// CUTSCENE_RESTART.
+CUTSCENE(MAIN_MENU_START_GAME, 0, DEFAULT,
+  CUTSCENE_MODAL(
+    "main_menu.checking_save.title",
+    "main_menu.checking_save.message"
+  ),
+  CUTSCENE_WAIT(0.2f),
+  CUTSCENE_SAVE_DEVICE_CHECK("CONTINUE", "NO_DEVICE"),
+
+  CUTSCENE_MARKER("NO_DEVICE"),
+  CUTSCENE_MODAL_CLOSE(),
+  CUTSCENE_MODAL_OPTIONS_TWO(
+    "main_menu.no_device.title",
+    "main_menu.no_device.message",
+    "main_menu.no_device.retry", "RETRY",
+    "main_menu.no_device.continue", "CONTINUE"
+  ),
+
+  CUTSCENE_MARKER("RETRY"),
+  CUTSCENE_MODAL_CLOSE(),
+  CUTSCENE_RESTART(),
+
+  CUTSCENE_MARKER("CONTINUE"),
+  CUTSCENE_MODAL_CLOSE(),
+  CUTSCENE_SAVE_LOAD_ALL_SLOTS("LOADED", "LOAD_ERROR"),
+
+  CUTSCENE_MARKER("LOAD_ERROR"),
+  CUTSCENE_MODAL_OPTIONS_ONE(
+    "main_menu.save_load_error.title",
+    "main_menu.save_load_error.message",
+    "main_menu.save_load_error.retry",
+    "RETRY"
+  ),
+
+  CUTSCENE_MARKER("LOADED"),
+  CUTSCENE_CALLBACK(sceneMainMenuOpenSelectSave)
+);
+
+void sceneMainMenuSelectSaveResult(const uint8_t slotIndex, void *user) {
+  if(slotIndex == UI_SELECT_SAVE_RESULT_NONE) {
+    uiMainMenuOpen();
+    return;
+  }
+
+  // TODO: load/start the game using the chosen save slot.
+  sceneSet(SCENE_TYPE_OVERWORLD);
+}
+
+void sceneMainMenuOpenSelectSave(void *userData) {
+  uiSelectSaveOpen(
+    UI_SELECT_SAVE_TYPE_LOAD, sceneMainMenuSelectSaveResult, NULL
+  );
+}
+
+void sceneMainMenuStartGame(void) {
+  cutsceneSystemStartCutscene(&CUTSCENE_MAIN_MENU_START_GAME);
+}
 
 errorret_t sceneMainMenuInit(scenedata_t *sceneData) {
   uiMainMenuOpen();

src/dusk/scene/mainmenu/scenemainmenu.h

@@ -8,7 +8,7 @@
 #pragma once
 #include "scene/scenebase.h"
 
-// Empty - the menu itself lives in ui/frame/mainmenu/uimainmenu.c. A byte
+// Empty - the menu itself lives in ui/screen/mainmenu/uimainmenu.c. A byte
 // placeholder keeps the struct non-empty for portability.
 typedef struct {
   uint8_t reserved;
@@ -22,6 +22,14 @@ typedef struct {
  */
 errorret_t sceneMainMenuInit(scenedata_t *sceneData);
 
+/**
+ * Starts the "Start Game" flow: runs a cutscene that loads every save
+ * slot (retrying on error, prompting if no save device is found) and
+ * opens the load-game picker once it succeeds. Called by
+ * ui/screen/mainmenu/uimainmenu.c when the player selects Start Game.
+ */
+void sceneMainMenuStartGame(void);
+
 /**
  * Updates the main menu scene. Currently a no-op - the menu drives
  * itself via the global UI element pipeline.

src/dusk/ui/screen/mainmenu/uimainmenu.c

@@ -16,80 +16,18 @@
 #include "locale/localemanager.h"
 #include "asset/loader/locale/assetlocaleloader.h"
 #include "ui/dialog/uiconfirm.h"
-#include "ui/dialog/save/uiselectsave.h"
+#include "scene/mainmenu/scenemainmenu.h"
-#include "rpg/cutscene/cutscene.h"
-#include "rpg/cutscene/cutscenesystem.h"
-#include "scene/scene.h"
 
 #define UI_MAIN_MENU_INDEX_START_GAME 0
 #define UI_MAIN_MENU_INDEX_OPTIONS 1
 #define UI_MAIN_MENU_INDEX_QUIT 2
 
-void uiMainMenuOpenSelectSave(void *userData);
-
-// Loads every save slot before opening the load-game picker, same
-// checking/retry-on-error shape as the initial scene's device lookup
-// (see scene/initial/sceneinitial.c) - the error branch loops back via
-// CUTSCENE_RESTART.
-CUTSCENE(MAIN_MENU_START_GAME, 0, DEFAULT,
-  CUTSCENE_MODAL(
-    "main_menu.checking_save.title",
-    "main_menu.checking_save.message"
-  ),
-  CUTSCENE_WAIT(0.2f),
-  CUTSCENE_SAVE_DEVICE_CHECK("CONTINUE", "NO_DEVICE"),
-
-  CUTSCENE_MARKER("NO_DEVICE"),
-  CUTSCENE_MODAL_CLOSE(),
-  CUTSCENE_MODAL_OPTIONS_TWO(
-    "main_menu.no_device.title",
-    "main_menu.no_device.message",
-    "main_menu.no_device.retry", "RETRY",
-    "main_menu.no_device.continue", "CONTINUE"
-  ),
-
-  CUTSCENE_MARKER("RETRY"),
-  CUTSCENE_MODAL_CLOSE(),
-  CUTSCENE_RESTART(),
-
-  CUTSCENE_MARKER("CONTINUE"),
-  CUTSCENE_MODAL_CLOSE(),
-  CUTSCENE_SAVE_LOAD_ALL_SLOTS("LOADED", "LOAD_ERROR"),
-
-  CUTSCENE_MARKER("LOAD_ERROR"),
-  CUTSCENE_MODAL_OPTIONS_ONE(
-    "main_menu.save_load_error.title",
-    "main_menu.save_load_error.message",
-    "main_menu.save_load_error.retry",
-    "RETRY"
-  ),
-
-  CUTSCENE_MARKER("LOADED"),
-  CUTSCENE_CALLBACK(uiMainMenuOpenSelectSave)
-);
-
 uimainmenu_t UI_MAIN_MENU;
 
 void uiMainMenuQuitConfirmed(const bool_t result, void *user) {
   if(result) ENGINE.running = false;
 }
 
-void uiMainMenuSelectSaveResult(const uint8_t slotIndex, void *user) {
-  if(slotIndex == UI_SELECT_SAVE_RESULT_NONE) {
-    uiMainMenuOpen();
-    return;
-  }
-
-  // TODO: load/start the game using the chosen save slot.
-  sceneSet(SCENE_TYPE_OVERWORLD);
-}
-
-void uiMainMenuOpenSelectSave(void *userData) {
-  uiSelectSaveOpen(
-    UI_SELECT_SAVE_TYPE_LOAD, uiMainMenuSelectSaveResult, NULL
-  );
-}
-
 void uiMainMenuSelected(
   const uimenu_t *menu,
   const uint8_t index,
@@ -99,7 +37,7 @@ void uiMainMenuSelected(
   switch(index) {
     case UI_MAIN_MENU_INDEX_START_GAME:
       uiMenuClose(&UI_MAIN_MENU.menu);
-      cutsceneSystemStartCutscene(&CUTSCENE_MAIN_MENU_START_GAME);
+      sceneMainMenuStartGame();
       break;
 
     case UI_MAIN_MENU_INDEX_OPTIONS: