Hold two frames on Oak's turn before the Pikachu battle starts

oak.facing was set and the battle pushed in the same synchronous
callback, so the overworld never rendered a frame of Oak already
turned toward the grass before the screen cut to battle.

Traced home/overworld.asm: PalletTownOakGreetsPlayerScript (the turn)
and PalletTownPikachuBattleScript (arming wCurOpponent) are separate
script ticks, one main-loop iteration apart. OverworldLoopLessDelay
burns two DelayFrame calls per iteration, calls RunMapScript (via
JoypadOverworld) first, and only then checks wCurOpponent to jump
into the battle -- so the turn from iteration A is on screen for the
two DelayFrame calls that open iteration B, before that same
iteration's RunMapScript arms wCurOpponent and falls straight into
the battle check. hold(2, ...) restores exactly that beat.

data/scripts/story2.lua

@@ -262,14 +262,27 @@ M.PALLET_TOWN = {
         function()
           -- Oak turns toward the horizontally adjacent grass (left exit
           -- looks right, right exit looks left -- the
-          -- EVENT_PLAYER_AT_RIGHT_EXIT_TO_PALLET_TOWN branch)
+          -- EVENT_PLAYER_AT_RIGHT_EXIT_TO_PALLET_TOWN branch).
+          -- PalletTownOakGreetsPlayerScript (the turn) and
+          -- PalletTownPikachuBattleScript (arming wCurOpponent) are
+          -- separate script ticks in pokeyellow, one main-loop iteration
+          -- apart: OverworldLoopLessDelay (home/overworld.asm) burns two
+          -- DelayFrame calls per iteration, calls RunMapScript (via
+          -- JoypadOverworld) first, and only then checks wCurOpponent to
+          -- jump into the battle -- so the turn from iteration A is on
+          -- screen for the two DelayFrame calls that open iteration B,
+          -- before that same iteration's RunMapScript arms wCurOpponent
+          -- and falls straight into the battle check. Two frames, not
+          -- zero and not a deliberate pause.
           if oak then oak.facing = x == 10 and "right" or "left" end
-          local battle = BattleState.newWild(game, "PIKACHU", 5)
-          battle:makeOldManDemo("PROF.OAK")
-          battle.onFinish = function()
-            afterPikaBattle()
-          end
-          game.stack:push(battle)
+          hold(2, nil, function()
+            local battle = BattleState.newWild(game, "PIKACHU", 5)
+            battle:makeOldManDemo("PROF.OAK")
+            battle.onFinish = function()
+              afterPikaBattle()
+            end
+            game.stack:push(battle)
+          end)
         end))
     end