Run the field-move white blink under its text, not after (#320)

The vanilla surf/strength flow closed the menu, showed the overworld,
then fired a solid-white blink on the empty map, and set the surfing
sprite while the player was still on land.  pokered's
GBPalWhiteOutWithDelay3 runs while the text is still up, so the blink
reads as a text flash.

The blink now sits under the textbox on the stack (only the top state
updates, so it holds its frames until the text closes), and surfing
applies only when the step onto the water happens.  Same reorder for
the party-menu STRENGTH texts.  The parity surf tests now dismiss the
got-on text before asserting the mount, matching the new order.

src/ui/PartyMenu.lua

@@ -304,10 +304,12 @@ function PartyMenu:update(dt)
           or Strings("{RAM:wNameBuffer} used\nSTRENGTH.")):gsub("{RAM:wNameBuffer}", name)
         local t2 = (self.game.data.text._CanMoveBouldersText
           or Strings("{RAM:wNameBuffer} can\nmove boulders.")):gsub("{RAM:wNameBuffer}", name)
+        -- like surf (#320): the blink belongs UNDER the texts, not as a
+        -- flashbang on the empty map after them; the stack only updates
+        -- the top state, so the flash holds until the texts close
+        self.game.stack:push(Transition.whiteFlash(self.game))
         self.game.stack:push(TextBox.new(self.game, t1, function()
-          self.game.stack:push(TextBox.new(self.game, t2, function()
-            self.game.stack:push(Transition.whiteFlash(self.game))
-          end))
+          self.game.stack:push(TextBox.new(self.game, t2))
         end, { auto = { sound = function()
           return require("src.core.Sound").playCry(self.game.data, mon.species)
         end } }))