Return to the start menu when a pause submenu is cancelled (#270) (#300)

Selecting a start-menu row pops the start menu before the submenu is
pushed (Menu's generic A handler), so B in a submenu had no parent to
return to and dropped straight to the overworld.  pokered redisplays
the start menu instead (RedisplayStartMenu from the party/item/
trainer-card/option handlers), so give each vanilla submenu an
onCancel that re-opens the start menu; the saved cursor row
(wBattleAndStartSavedMenuItem) restores on re-entry.

- PokedexMenu/BagMenu forward opts.onCancel into their ListMenu
- TrainerCard dismisses back via onCancel on A or B
  (WaitForTextScrollButtonPress then RedisplayStartMenu)
- OptionsMenu fires onCancel from both B/START and the CANCEL row
- PlayerPC rows are keepOpen so B in WITHDRAW/DEPOSIT/TOSS returns to
  the PC root menu (players_pc.asm), matching the BoxMenu pattern

The SAVE flow is untouched: StartMenu_SaveReset falls through to
HoldTextDisplayOpen and never redisplays the menu.  Battle-opened
party/bag screens get no onCancel, so mid-battle cancel behavior is
unchanged.

Co-authored-by: johnjohto <johnjohto@users.noreply.github.com>

src/ui/BagMenu.lua

@@ -372,6 +372,8 @@ function BagMenu.new(game, opts)
   list = ListMenu.new(game, "ITEMS", buildItems(game), {
     kind = "bag",
     footer = ("¥%d"):format(game.save.money),
+    -- B returns to the start menu when the bag was opened from it
+    onCancel = opts.onCancel,
     -- SELECT reorders items like the original bag (swap_items.asm)
     onSelectKey = function(item, l)
       if not item then return end