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/PokedexMenu.lua

@@ -9,7 +9,8 @@ function PokedexMenu:sgbPalettes(game)
   return require("src.render.PaletteFX").wholeNamed(game.data, "BROWNMON")
 end
 
-function PokedexMenu.new(game)
+function PokedexMenu.new(game, opts)
+  opts = opts or {}
   local dex = game.save.pokedex or { seen = {}, owned = {} }
   local byDex = {}
   for species, def in pairs(game.data.pokemon) do
@@ -47,6 +48,7 @@ function PokedexMenu.new(game)
   local list = ListMenu.new(game, "POKéDEX", items, {
     footer = ("SEEN %d  OWNED %d"):format(seen, owned),
     pageJump = true, -- Left/Right page jumps like the original
+    onCancel = opts.onCancel, -- B returns to the start menu when opened from it
     onChoose = function(item)
       if not item.value then return end
       -- the DATA / CRY / AREA / QUIT choice (engine/menus/pokedex.asm