Add declarative cutscene items for save checks and marker-based modals

CUTSCENE_SAVE_DEVICE_CHECK and CUTSCENE_SAVE_LOAD_ALL_SLOTS wrap the
existing device-lookup/slot-load calls and jump straight to a
success/failure marker, and CUTSCENE_MODAL_OPTIONS_ONE/TWO do the same
for one/two-option modals, removing the need for a hand-written
goTo-only callback per use. Main menu's "Start Game" now runs a
cutscene (mirroring the initial scene's save-check flow) that loads all
slots before opening the load-game picker, retrying on error; the
initial scene's own device check is migrated onto the same items.
Backing out of the main menu now returns to the initial scene.

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

assets/locale/en_US.po

@@ -38,6 +38,33 @@ msgstr "Quit Game"
 msgid "main_menu.quit_confirm"
 msgstr "Are you sure you want to quit?"
 
+msgid "main_menu.checking_save.title"
+msgstr "Checking for save data"
+
+msgid "main_menu.checking_save.message"
+msgstr "Please wait..."
+
+msgid "main_menu.no_device.title"
+msgstr "No Save Device Found"
+
+msgid "main_menu.no_device.message"
+msgstr "Could not find a save device, ensure it is connected and try again. You can continue, but progress will not be saved."
+
+msgid "main_menu.no_device.retry"
+msgstr "Try again"
+
+msgid "main_menu.no_device.continue"
+msgstr "Continue without saving"
+
+msgid "main_menu.save_load_error.title"
+msgstr "Error"
+
+msgid "main_menu.save_load_error.message"
+msgstr "Failed to load save data. Please try again."
+
+msgid "main_menu.save_load_error.retry"
+msgstr "Try Again"
+
 
 # Select Save Screen
 msgid "ui.select_save.title"